M10: BigTIFF and strict GIF detection in Create PDF; XDP data in format parity (#1453)

- Create PDF detects BigTIFF (II+/MM+) as well as classic TIFF; the tiff
  decoder already reads it, so these scans now convert instead of being
  refused.
- Image detection accepts only GIF87a/GIF89a, the headers conversion
  decodes, so a malformed GIF header is no longer called an image and then
  rejected with a misleading error.
- file-format-parity.md: XDP split into XFA data import/export (shipped
  under form.xfa-data) and opening .xdp as a document (none).

Tests: bigtiff_images_become_pages; malformed GIF headers in
source_kind_tells_pdfs_images_and_text_apart. Both fail without the fix.


Claude-Session: https://claude.ai/code/session_01F8DFYWkDyTnEcin9PNkUW5

Co-authored-by: Claude <[email protected]>
Co-authored-by: Brandon Thomas <[email protected]>

docs/file-format-parity.md

@@ -1,6 +1,6 @@
 # File format parity
 
-> **Last reviewed:** 2026-10-10 · **Last updated:** 2026-10-11 · **Change:** minor (Word invoice export, #773; encrypted output opens in Acrobat, #774; XFDF fixes #807, #809, #819) · **Target:** Adobe Acrobat Pro (Acrobat DC, continuous track 26.002.21931, macOS)
+> **Last reviewed:** 2026-10-12 · **Last updated:** 2026-10-12 · **Change:** minor (XDP data row corrected; BigTIFF in Create PDF) · **Target:** Adobe Acrobat Pro (Acrobat DC, continuous track 26.002.21931, macOS)
 
 Every format Acrobat Pro reads or writes, and PdfCraft's support for it. Acrobat's list comes from
 its bundle's `Info.plist` `CFBundleDocumentTypes` (what it opens) and its public documentation
@@ -38,7 +38,8 @@ features total).
 | FDF (`.fdf`) comments and form data | R W | R W | good | `crates/xfdf`; comment-exchange fixes for popups, polygon vertices and callouts (#807, #809, #819) |
 | XFDF (`.xfdf`, ISO 19444-1) | R W | R W | good | as above |
 | XML form data | R W | R W | good | `form.data-xml-csv-txt` |
-| XDP (`.xdp`, XFA data package) | R | none | none | Acrobat opens `.xdp` as a document type |
+| XDP data (`.xdp`) for XFA forms | R W | R W: Export Data writes the whole datasets as an XDP; Import Data takes an XDP, datasets or data XML | good | `form.xfa-data` (`data_exports_as_datasets_xml_or_an_xdp_and_imports_from_any_of_them`, `xfa_data_files_export_and_import_through_tools`) |
+| XDP opened as a document | R | none | none | Acrobat opens `.xdp` as a document type |
 | CSV / tab-delimited form data | W (merge to spreadsheet) | R W; merge to spreadsheet | good | `form.merge-to-spreadsheet` |
 | Comment summary (PDF) | W | W (comments only layout) | basic | `comment.summarize` partial |
 | Measurement CSV | W | W | good | `comment.measure-export` |
@@ -62,7 +63,7 @@ features total).
 
 | Source | Acrobat | PdfCraft | Fidelity | Tests and evidence |
 |---|---|---|---|---|
-| JPEG, PNG, TIFF (multipage), GIF, BMP, JPEG 2000 | yes | yes (ICC profiles kept; DPI choices) | good | `create.from-images`, `create.from-multipage-tiff` |
+| JPEG, PNG, TIFF (multipage, and BigTIFF), GIF, BMP, JPEG 2000 | yes | yes (ICC profiles kept; DPI choices) | good | `create.from-images`, `create.from-multipage-tiff`, `bigtiff_images_become_pages` |
 | PCX | yes | no | none | in Acrobat's document types |
 | Plain text | yes | yes | good | `create.from-text` |
 | Clipboard (image or text) | yes | yes | good | `create.from-clipboard` |
@@ -109,6 +110,7 @@ features total).
 
 | Date | Change | Summary |
 |---|---|---|
+| 2026-10-12 | minor | XDP split into data (read and write for XFA forms, already shipped under `form.xfa-data`) and opening `.xdp` as a document (none). Create PDF reads BigTIFF; malformed GIF headers are no longer detected as images. |
 | 2026-10-11 | minor | #773: inferred tables have no invented borders; rotated or overlapping invoice pages use floating shapes and page sections. Full Office layout fidelity remains partial. |
 | 2026-10-11 | minor | Encrypted PDF row: written files open in Acrobat DC (#774, fixed by #836). FDF row: #807, #809 and #819 fixed |
 | 2026-10-10 | major | Created from Acrobat 26.002.21931's `CFBundleDocumentTypes`, Acrobat's public Create/Export documentation, and PdfCraft's code and checklist |