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# pdfcraft-xfdf
Layer L4: comment and form data exchange (execution plan M5.6, M6.7).
```rust
let xml = export_xfdf(&doc, true, true, "form.pdf"); // comments and/or field values
let fdf = export_fdf(&doc, false, true, "form.pdf");
let txt = export_data(&doc, Format::Txt); // or Xml, Csv
let report = import(&mut doc, &bytes)?; // XFDF, FDF, XML, CSV or text, detected
```
- **XFDF** (ISO 19444-1): every comment type PdfCraft knows (text, free text, line, square,
circle, polygon, polyline, markup, stamp, caret, ink, attachments, sound, redact) with rect,
name, author, subject, dates, flags, colours, opacity, width, icon, quads, line ends, ink,
default appearance, callouts (`callout`, `fringe`, `intent`, `head`), pop-ups and reply threads
(`inreplyto`); field values nested by name, with text preserved across XML comments and processing instructions.
- **FDF**: fields (with `/Kids` hierarchies) and comments as direct objects.
- **Form data**: Acrobat's XML (`xfdf:original` keeps names that aren't XML names), CSV and
tab-delimited text (a row of names, a row of values).
XML and XFDF exports preserve tabs and line breaks in field names and comment metadata with
character references, so XML attribute normalization cannot change their identities.
Plain AcroForm XML imports retain all direct text around comments and processing instructions,
including CDATA and character references. Nested-element and XFA interpretation are unchanged.
CSV export and spreadsheet merging quote tabs, and import distinguishes quoted tabs from TSV
delimiters without changing field identities. Automatic detection of externally authored, ambiguous
tables remains heuristic.
Import replaces comments with the same `/NM` (and drops the replaced comment's pop-up), draws
appearances PdfCraft can draw, and sets values through the form's own checks (formats,
validation, recalculation); read-only fields take imported values, as in Acrobat. XML is read
with `roxmltree`.