pdfcraft/crates/annot/README.md

pdfcraft-annot

Comments (annotations), ISO 32000-2 §12.5. Layer L3, depends on pdfcraft-cos, pdfcraft-fonts and pdfcraft-model.

What it does

• Builders for the comment types Acrobat's commenting tools create: sticky note (Text + Popup), highlight, underline, strikethrough, squiggly, rectangle (Square), oval (Circle), line and arrow (Line with /LE), freehand drawing (Ink) and text box (FreeText).
• Appearance streams (appearance::build) generated from the annotation dictionary, so new and restyled comments look the same in every viewer. Highlights multiply (/BM /Multiply). Note icons are PdfCraft's own drawings. Text boxes use standard Helvetica (WinAnsi), with line breaking by approximate Helvetica proportions (no font program is bundled). Text it can't draw (in a text box, callout, Fill & Sign text, measurement label or dynamic stamp's by-line; appearance::undrawable_text) is kept as typed and drawn as ?, and the comment is marked with the first such character (pdfcraft_fonts::UNDRAWN_MARK) so the engine reports the edit and flattening refuses to make it permanent. Two refusals (AnnotError::Undrawable): a redaction mark's overlay text, which becomes page content when applied; and a restyle or resize of a comment another program drew with a font that has those characters, whose appearance is kept rather than redrawn with ? (new text for it is taken).
• Edits: reply (/IRT), set review status (a /State reply, as Acrobat's "Set status" does), change text, move, resize, restyle, delete (with pop-up and replies).

API sketch

let index = add_annotation(&mut doc, &NewAnnotation { page, shape, style, contents, author }, &meta)?;
add_reply(&mut doc, page, index, "Agreed", "Ada", &meta)?;
set_review_state(&mut doc, page, index, ReviewState::Accepted, "Ada", &meta)?;
move_annotation(&mut doc, page, index, dx, dy, &meta)?;
set_style(&mut doc, page, index, Some(rgb), Some(0.5), Some(2.0), &meta)?;
delete_annotation(&mut doc, page, index)?;
signature_image(&doc, page, index)?; // embedded image XObject of Fill & Sign signature/initials

A comment is addressed by (page, index in /Annots), the same pair pdfcraft_render::Annotation reports. Meta carries the date and the /NM id so edits stay deterministic; the engine supplies them.

Fidelity rules

• Unknown keys are kept. Inline annotation dictionaries are promoted to indirect objects only when an edit needs a reference to them.
• set_style refuses (and changes nothing) when it cannot redraw the comment, e.g. stamps, cloudy borders or callouts, instead of leaving a stale appearance.
• Replies get the parent's /Rect and an empty appearance: they appear in comment lists but never paint a second icon.
• Resizing a stamp changes its /Rect and preserves its original appearance and resources; viewers scale that appearance into the new rectangle. Locked stamps refuse the edit.
• Picture stamps (a natural-size or explicit-rectangle image, a PDF page, or an image signature) and PdfCraft's rubber stamps counterrotate their appearance on rotated pages, so the picture or label reads upright as the page is displayed. Restyling a picture stamp keeps that appearance matrix. The rotation is the page's /Rotate at placement.

Not yet

Callouts, polygons and polylines, clouds, carets (insert/replace text), stamps, file attachments, rich text (/RC, /DS), and the shared named-appearance cache Acrobat writes.