diff --git a/apps/ely-pdf/src/visible.rs b/apps/ely-pdf/src/visible.rs
index 404cf2d..688dbd7 100644
--- a/apps/ely-pdf/src/visible.rs
+++ b/apps/ely-pdf/src/visible.rs
@@ -95,6 +95,7 @@ impl PdfView {
                 let write = move |worker: &mut ely_pdf_engine::Worker, doc| match worker.put_text(doc, page, &writing, 0.0)? {
                     Wrote::Done(mark) => Ok(mark),
                     Wrote::Missing(c) => Err(io::Error::new(io::ErrorKind::InvalidInput, format!("the font has no “{c}”"))),
+                    Wrote::Unwritable => Err(io::Error::other("the document's font cannot write")),
                     Wrote::Preview(..) => Err(io::Error::other("a preview where a write was asked")),
                 };
                 self.edit_at("placing a typed signature", write, cx);
diff --git a/apps/ely-pdf/src/writes.rs b/apps/ely-pdf/src/writes.rs
index 59bda49..c2b7ce5 100644
--- a/apps/ely-pdf/src/writes.rs
+++ b/apps/ely-pdf/src/writes.rs
@@ -96,6 +96,13 @@ impl Viewer {
         cx: &mut Context<Self>,
     ) {
         match answer {
+            Ok(Wrote::Unwritable) => {
+                let note = Self::text(cx, "pdf.text.unwritable", &[]);
+                self.edit_panel.update(cx, |panel, cx| {
+                    panel.note = Some(note);
+                    cx.notify();
+                });
+            }
             Ok(Wrote::Missing(c)) => {
                 let note = Self::text(cx, "pdf.text.missing", &[("char", &c.to_string())]);
                 self.edit_panel.update(cx, |panel, cx| {
@@ -128,6 +135,7 @@ impl Viewer {
                 move |worker, doc| match worker.put_text(doc, page, &writing, 0.0)? {
                     Wrote::Done(mark) => Ok(mark),
                     Wrote::Missing(c) => Err(io::Error::other(format!("the font has no {c}"))),
+                    Wrote::Unwritable => Err(io::Error::other("the document's font cannot write")),
                     Wrote::Preview(..) => Err(io::Error::other("a write came back as a preview")),
                 },
                 cx,
diff --git a/crates/ely-pdf-engine/shim/ely_pen.c b/crates/ely-pdf-engine/shim/ely_pen.c
index 6af5ccd..695fbe0 100644
--- a/crates/ely-pdf-engine/shim/ely_pen.c
+++ b/crates/ely-pdf-engine/shim/ely_pen.c
@@ -29,13 +29,13 @@ static int unicode_of(pdf_font_desc *desc, int cid)
 	return n == 1 && ucs[0] > 0 && ucs[0] != FZ_REPLACEMENT_CHARACTER ? ucs[0] : -1;
 }
 
-/* Unicode and code pairs of `desc`; its codes are CIDs. */
-static void own_codes(fz_context *ctx, pdf_font_desc *desc, ely_pen *p)
+/* `desc` Unicode-to-code pairs; -1 when codes are not CIDs. */
+static int own_codes(fz_context *ctx, pdf_font_desc *desc, ely_pen *p)
 {
 	pdf_cmap *enc = desc->encoding;
 	int cid, end;
 	if (!enc || strcmp(enc->cmap_name, "Identity-H") || enc->codespace_len != 1 || enc->codespace[0].n > 2)
-		fz_throw(ctx, FZ_ERROR_ARGUMENT, "the document's font uses codes Ely cannot write");
+		return -1;
 	p->bytes = enc->codespace[0].n;
 	end = 1 << (8 * p->bytes);
 	p->map = fz_malloc_array(ctx, 2 * end, int);
@@ -45,10 +45,11 @@ static void own_codes(fz_context *ctx, pdf_font_desc *desc, ely_pen *p)
 		if (u > 0 && pdf_font_cid_to_gid(ctx, desc, cid) > 0)
 			p->map[2 * p->mapped] = u, p->map[2 * p->mapped + 1] = cid, p->mapped++;
 	}
+	return 0;
 }
 
-/* The page font drawn as `own`, with its codes. */
-static void own_font(fz_context *ctx, pdf_page *page, fz_font *own, ely_pen *p)
+/* The page font drawn as `own`; -1: cannot write. */
+static int own_font(fz_context *ctx, pdf_page *page, fz_font *own, ely_pen *p)
 {
 	pdf_obj *res = pdf_page_resources(ctx, page);
 	pdf_resource_stack stack = { NULL, res };
@@ -63,16 +64,15 @@ static void own_font(fz_context *ctx, pdf_page *page, fz_font *own, ely_pen *p)
 			continue;
 		}
 		p->desc = desc;
+		/* A direct font cannot be named again after the edit. */
 		p->num = pdf_to_num(ctx, pdf_dict_get_val(ctx, fonts, i));
-		if (!p->num)
-			fz_throw(ctx, FZ_ERROR_ARGUMENT, "the document's font is not an object of its own");
-		own_codes(ctx, desc, p);
+		return p->num ? own_codes(ctx, desc, p) : -1;
 	}
-	if (!p->desc)
-		fz_throw(ctx, FZ_ERROR_ARGUMENT, "the block's font is not a font of its page");
+	/* Drawn from elsewhere, as in a form: not writable here. */
+	return -1;
 }
 
-void ely_choose_pen(fz_context *ctx, const char *choice, fz_font *own, pdf_page *page, ely_pen *p)
+int ely_choose_pen(fz_context *ctx, const char *choice, fz_font *own, pdf_page *page, ely_pen *p)
 {
 	static const struct { const char *choice, *name; } latin[] = {
 		{ "helvetica", "Helvetica" }, { "times", "Times-Roman" }, { "courier", "Courier" } };
@@ -85,22 +85,21 @@ void ely_choose_pen(fz_context *ctx, const char *choice, fz_font *own, pdf_page
 			fz_throw(ctx, FZ_ERROR_ARGUMENT, "no script font was given");
 		p->kind = PEN_CID;
 		p->font = fz_new_font_from_memory(ctx, "GreatVibes", script_data, (int)script_len, 0, 0);
-		return;
+		return 0;
 	}
 	if (!strcmp(choice, "original"))
 	{
 		if (!own)
 			fz_throw(ctx, FZ_ERROR_ARGUMENT, "the block has no font of its own");
 		p->kind = PEN_OWN;
-		own_font(ctx, page, own, p);
-		return;
+		return own_font(ctx, page, own, p);
 	}
 	for (i = 0; i < nelem(latin); i++)
 		if (!strcmp(choice, latin[i].choice))
 		{
 			p->kind = PEN_SIMPLE;
 			p->font = fz_new_base14_font(ctx, latin[i].name);
-			return;
+			return 0;
 		}
 	for (i = 0; i < nelem(cjk); i++)
 		if (!strcmp(choice, cjk[i].choice))
@@ -108,7 +107,7 @@ void ely_choose_pen(fz_context *ctx, const char *choice, fz_font *own, pdf_page
 			p->kind = PEN_CJK;
 			p->ordering = cjk[i].ordering;
 			p->font = fz_new_cjk_font(ctx, cjk[i].ordering);
-			return;
+			return 0;
 		}
 	fz_throw(ctx, FZ_ERROR_ARGUMENT, "no font %s", choice);
 }
diff --git a/crates/ely-pdf-engine/shim/ely_shim.h b/crates/ely-pdf-engine/shim/ely_shim.h
index 2e2ba80..be74d80 100644
--- a/crates/ely-pdf-engine/shim/ely_shim.h
+++ b/crates/ely-pdf-engine/shim/ely_shim.h
@@ -76,7 +76,7 @@ typedef struct
 	int *map, mapped;
 } ely_pen;
 
-void ely_choose_pen(fz_context *ctx, const char *choice, fz_font *own, pdf_page *page, ely_pen *p);
+int ely_choose_pen(fz_context *ctx, const char *choice, fz_font *own, pdf_page *page, ely_pen *p);
 const char *ely_pen_resource(fz_context *ctx, pdf_document *pdf, pdf_page *page, ely_pen *p, char *name, size_t room);
 int ely_pen_has(fz_context *ctx, ely_pen *p, int u);
 float ely_pen_advance(fz_context *ctx, ely_pen *p, int u, float size);
diff --git a/crates/ely-pdf-engine/shim/ely_write.c b/crates/ely-pdf-engine/shim/ely_write.c
index bb1f551..1766870 100644
--- a/crates/ely-pdf-engine/shim/ely_write.c
+++ b/crates/ely-pdf-engine/shim/ely_write.c
@@ -156,11 +156,12 @@ static void drop_laid(fz_context *ctx, laid *l)
 	fz_free(ctx, l->to);
 }
 
-/* Lays `a` out from `first`, or names a missing glyph. */
+/* Lays `a` out; a missing glyph, or -1: unwritable font. */
 static int lay_text(fz_context *ctx, text_args *a, fz_font *own, pdf_page *page, fz_point first, float gap, laid *l)
 {
 	int i;
-	ely_choose_pen(ctx, a->font, own, page, &l->p);
+	if (ely_choose_pen(ctx, a->font, own, page, &l->p) < 0)
+		return -1;
 	l->n = runes(ctx, a->text, &l->u);
 	for (i = 0; i < l->n; i++)
 		if (l->u[i] != '\n' && !ely_pen_has(ctx, &l->p, l->u[i]))
@@ -259,7 +260,7 @@ static void preview(fz_context *ctx, pdf_document *pdf, int number, int block, c
 		fz_rethrow(ctx);
 }
 
-/* Edits, adds or previews text: 0, 2 missing, -1 failed. */
+/* Writes or previews text: 0, 2 missing, 3 unwritable, -1. */
 int ely_put_text(fz_context *ctx, fz_document *doc, int number, int block, const char *expected, const char *text,
 	const char *font, float size, int rgb, const float box[3], const char *password, float scale, int *missing,
 	int *grew, unsigned char **pixels, int *w, int *h)
@@ -325,5 +326,5 @@ int ely_put_text(fz_context *ctx, fz_document *doc, int number, int block, const
 		*pixels = NULL;
 		return ely_edit_failed(ctx, pdf, begun);
 	}
-	return *missing ? 2 : 0;
+	return *missing < 0 ? 3 : *missing ? 2 : 0;
 }
diff --git a/crates/ely-pdf-engine/src/bin/ely-pdf-worker/content.rs b/crates/ely-pdf-engine/src/bin/ely-pdf-worker/content.rs
index 2175f2a..ca531d6 100644
--- a/crates/ely-pdf-engine/src/bin/ely-pdf-worker/content.rs
+++ b/crates/ely-pdf-engine/src/bin/ely-pdf-worker/content.rs
@@ -59,6 +59,8 @@ pub enum Wrote {
     Done,
     /// A character the font cannot draw; nothing changed.
     Missing(char),
+    /// The document's own font cannot write; nothing changed.
+    Unwritable,
     /// The would-be result: BGRA, size, and whether it grew.
     Preview(Vec<u8>, (u32, u32), bool),
 }
@@ -106,6 +108,9 @@ impl Mupdf {
                 &mut height,
             )
         })?;
+        if status == 3 {
+            return Ok(Wrote::Unwritable);
+        }
         if status == 2 {
             let missing = u32::try_from(missing).ok().and_then(char::from_u32);
             return Ok(Wrote::Missing(missing.ok_or_else(|| io::Error::other("a missing glyph out of range"))?));
diff --git a/crates/ely-pdf-engine/src/bin/ely-pdf-worker/main.rs b/crates/ely-pdf-engine/src/bin/ely-pdf-worker/main.rs
index 9ffbd95..f0f3432 100644
--- a/crates/ely-pdf-engine/src/bin/ely-pdf-worker/main.rs
+++ b/crates/ely-pdf-engine/src/bin/ely-pdf-worker/main.rs
@@ -147,6 +147,7 @@ impl Worker {
         Ok(match wrote? {
             content::Wrote::Done => Pack::new().u64(0).str(&doc.mark()).bytes(),
             content::Wrote::Missing(c) => Pack::new().u64(2).u64(u64::from(c)).bytes(),
+            content::Wrote::Unwritable => Pack::new().u64(3).bytes(),
             content::Wrote::Preview(pixels, (w, h), grew) => {
                 Pack::new().u64(1).u64(u64::from(w)).u64(u64::from(h)).u64(u64::from(grew)).blob(&pixels).bytes()
             }
diff --git a/crates/ely-pdf-engine/src/content.rs b/crates/ely-pdf-engine/src/content.rs
index 7d63c0f..98e4728 100644
--- a/crates/ely-pdf-engine/src/content.rs
+++ b/crates/ely-pdf-engine/src/content.rs
@@ -49,6 +49,8 @@ pub enum Wrote {
     Done(String),
     /// The font lacks this character; nothing changed.
     Missing(char),
+    /// The document's own font cannot write; nothing changed.
+    Unwritable,
     /// BGRA of the area, its size, whether text grew.
     Preview(Vec<u8>, (u32, u32), bool),
 }
@@ -113,11 +115,13 @@ impl Worker {
                 let code = u32::try_from(reply.u64()?).map_err(io::Error::other)?;
                 Ok(Wrote::Missing(char::from_u32(code).ok_or_else(|| io::Error::other("a bad missing glyph"))?))
             }
-            _ => {
+            1 => {
                 let size = (reply.u64()? as u32, reply.u64()? as u32);
                 let grew = reply.u64()? != 0;
                 Ok(Wrote::Preview(reply.blob()?, size, grew))
             }
+            3 => Ok(Wrote::Unwritable),
+            other => Err(io::Error::other(format!("a text reply of kind {other}"))),
         }
     }
 
diff --git a/crates/ely-pdf-engine/tests/fonts.rs b/crates/ely-pdf-engine/tests/fonts.rs
new file mode 100644
index 0000000..e55ce82
--- /dev/null
+++ b/crates/ely-pdf-engine/tests/fonts.rs
@@ -0,0 +1,100 @@
+//! Fonts the editor meets in the wild (PDF-03).
+
+use std::path::Path;
+
+use ely_pdf_engine::{Doc, Worker, Writing, Wrote};
+
+fn worker() -> Worker {
+    Worker::spawn_from(Path::new(env!("CARGO_BIN_EXE_ely-pdf-worker"))).expect("the worker")
+}
+
+fn page_text(worker: &mut Worker, doc: Doc) -> String {
+    worker.text(doc, 0).expect("reads").iter().map(|c| c.c).collect()
+}
+
+/// A rewrite of block `block` as `text` in `font`.
+fn rewrite(worker: &mut Worker, doc: Doc, block: usize, text: &str, font: &str) -> Writing {
+    let read = worker.text_blocks(doc, 0).expect("blocks")[block].clone();
+    Writing {
+        block: Some(block),
+        expected: read.text,
+        text: text.into(),
+        font: font.into(),
+        size: read.size,
+        rgb: read.rgb,
+        bx: [read.rect[0], read.rect[1], read.rect[2] - read.rect[0]],
+    }
+}
+
+/// A page whose text uses a CMap-encoded CID font.
+fn cmap_font_pdf() -> Vec<u8> {
+    let content = "BT /F1 24 Tf 72 700 Td <00480069> Tj ET";
+    one_font_page(content, &[
+        "<< /Type /Font /Subtype /Type0 /BaseFont /STSong-Light /Encoding /UniGB-UCS2-H /DescendantFonts [6 0 R] >>".to_string(),
+        "<< /Type /Font /Subtype /CIDFontType0 /BaseFont /STSong-Light /CIDSystemInfo << /Registry (Adobe) /Ordering (GB1) /Supplement 2 >> /FontDescriptor 7 0 R >>".to_string(),
+        "<< /Type /FontDescriptor /FontName /STSong-Light /Flags 4 /FontBBox [0 -200 1000 900] /ItalicAngle 0 /Ascent 880 /Descent -120 /CapHeight 700 /StemV 80 >>".to_string(),
+    ])
+}
+
+/// A page drawing `content`; font objects start at 5.
+fn one_font_page(content: &str, font: &[String]) -> Vec<u8> {
+    page_with("<< /F1 5 0 R >>", content, font)
+}
+
+/// A page with font resources `fonts`; objects from 5.
+fn page_with(fonts: &str, content: &str, font: &[String]) -> Vec<u8> {
+    let mut objects = vec![
+        "<< /Type /Catalog /Pages 2 0 R >>".to_string(),
+        "<< /Type /Pages /Kids [3 0 R] /Count 1 >>".to_string(),
+        format!("<< /Type /Page /Parent 2 0 R /MediaBox [0 0 612 792] /Resources << /Font {fonts} >> /Contents 4 0 R >>"),
+        format!("<< /Length {} >>\nstream\n{content}\nendstream", content.len()),
+    ];
+    objects.extend_from_slice(font);
+    let mut pdf = b"%PDF-1.7\n".to_vec();
+    let mut offsets = Vec::new();
+    for (i, body) in objects.iter().enumerate() {
+        offsets.push(pdf.len());
+        pdf.extend(format!("{} 0 obj\n{body}\nendobj\n", i + 1).bytes());
+    }
+    let xref = pdf.len();
+    pdf.extend(format!("xref\n0 {}\n0000000000 65535 f \n", objects.len() + 1).bytes());
+    for offset in offsets {
+        pdf.extend(format!("{offset:010} 00000 n \n").bytes());
+    }
+    pdf.extend(format!("trailer\n<< /Size {} /Root 1 0 R >>\nstartxref\n{xref}\n%%EOF\n", objects.len() + 1).bytes());
+    pdf
+}
+
+#[test]
+fn a_font_whose_codes_ely_cannot_write_says_so() {
+    let dir = tempfile::tempdir().expect("a temp dir");
+    let path = dir.path().join("cmap.pdf");
+    std::fs::write(&path, cmap_font_pdf()).expect("writes");
+    let mut worker = worker();
+    let doc = worker.open(&path).expect("opens").doc;
+    assert_eq!(page_text(&mut worker, doc), "Hi");
+    let writing = rewrite(&mut worker, doc, 0, "Yo", "original");
+    assert_eq!(worker.put_text(doc, 0, &writing, 2.0).expect("answers"), Wrote::Unwritable);
+    assert_eq!(page_text(&mut worker, doc), "Hi", "nothing changed");
+    let helvetica = rewrite(&mut worker, doc, 0, "Yo", "helvetica");
+    assert!(matches!(worker.put_text(doc, 0, &helvetica, 0.0).expect("writes"), Wrote::Done(_)));
+}
+
+#[test]
+fn a_font_written_into_the_page_says_it_cannot_write() {
+    let dir = tempfile::tempdir().expect("a temp dir");
+    let path = dir.path().join("direct.pdf");
+    // The font dictionary sits in the page itself.
+    let fonts = "<< /F1 << /Type /Font /Subtype /Type0 /BaseFont /STSong-Light /Encoding /Identity-H /DescendantFonts [5 0 R] >> >>";
+    let pdf = page_with(fonts, "BT /F1 24 Tf 72 700 Td <00480069> Tj ET", &[
+        "<< /Type /Font /Subtype /CIDFontType0 /BaseFont /STSong-Light /CIDSystemInfo << /Registry (Adobe) /Ordering (GB1) /Supplement 2 >> /FontDescriptor 6 0 R >>".to_string(),
+        "<< /Type /FontDescriptor /FontName /STSong-Light /Flags 4 /FontBBox [0 -200 1000 900] /ItalicAngle 0 /Ascent 880 /Descent -120 /CapHeight 700 /StemV 80 >>".to_string(),
+    ]);
+    std::fs::write(&path, pdf).expect("writes");
+    let mut worker = worker();
+    let doc = worker.open(&path).expect("opens").doc;
+    let writing = rewrite(&mut worker, doc, 0, "Yo", "original");
+    assert_eq!(worker.put_text(doc, 0, &writing, 2.0).expect("answers"), Wrote::Unwritable);
+    let helvetica = rewrite(&mut worker, doc, 0, "Yo", "helvetica");
+    assert!(matches!(worker.put_text(doc, 0, &helvetica, 0.0).expect("writes"), Wrote::Done(_)));
+}
diff --git a/crates/ely-ui/src/i18n/pdf.rs b/crates/ely-ui/src/i18n/pdf.rs
index 557b175..c17ab7b 100644
--- a/crates/ely-ui/src/i18n/pdf.rs
+++ b/crates/ely-ui/src/i18n/pdf.rs
@@ -67,6 +67,7 @@ pub(super) const EN: &[(&str, &str)] = &[
         "pdf.text.missing",
         "This font cannot draw “{char}”. Choose another font.",
     ),
+    ("pdf.text.unwritable", "The document's own font cannot write new text. Choose another font."),
     ("pdf.object.replace", "Replace Image…"),
     ("pdf.object.delete", "Delete"),
     (
@@ -288,6 +289,7 @@ pub(super) const ZH_CN: &[(&str, &str)] = &[
     ("pdf.text.apply", "应用"),
     ("pdf.text.erase", "删除文字"),
     ("pdf.text.missing", "这种字体画不出“{char}”。请换一种字体。"),
+    ("pdf.text.unwritable", "文档自带的字体写不了新字。请换一种字体。"),
     ("pdf.object.replace", "替换图片…"),
     ("pdf.object.delete", "删除"),
     ("pdf.object.changed", "文档已改动，未执行。"),
diff --git a/tasks/BUGS.md b/tasks/BUGS.md
index 2e53471..b49a34a 100644
--- a/tasks/BUGS.md
+++ b/tasks/BUGS.md
@@ -38,7 +38,7 @@
 - [x] P-03 “编辑文字和图片”先命中图片对象再命中文字；一点抖动就移动了背景图 — 包住文字块的对象让位于文字，移动须过 3 个窗口像素；R1 漏掉同点的小图；R2 PASS
 - [x] P-04 `TEXT_BLOCKS` 对每个文字块重跑一遍整页内容过滤，编辑工具长时间无反应 — 整页一遍干跑判定全部文字块（1000 块 1.5 s→0.1 s）；R1 转向文字后错位、共用原点只计一块；R2 PASS
 - [x] P-05 连续快画或快点被拒：“文档在此间已改动，未执行” — 按坐标的编辑排队、跑在出队时的状态上，只在页面变动时拒绝；R2 PASS
-- [ ] P-06 默认字体“原字体”在 Type 1/Type 3 字体的文件上失败，只给引擎原话
+- [x] P-06 默认字体“原字体”在 Type 1/Type 3 字体的文件上失败，只给引擎原话 — 原字体写不了新字（非 CID 编码、页面内直接字体、不在本页）时面板提示换字体；R2 PASS
 - [ ] P-07 含连字的文字块永远不可编辑
 - [ ] P-08 页面读取失败后每帧重试、每帧弹提示
 - [ ] P-09 识别文字的写入被拒后仍弹“成功”