pdfcraft/crates/redact/README.md

pdfcraft-redact

Layer L4 (may use edit): redaction, architecture §11.2.

// Marks are Redact annotations (pdfcraft-annot: Shape::Redact { quads, overlay }).
let marks: Vec<Mark> = marks(&doc);                 // page, areas (user space), fill, overlay text
let report = apply(&mut doc, None)?;                 // everything, or Some(&[pages])
clear_marks(&mut doc, None)?;                        // remove marks without applying

apply removes, under every marked area:

• text: glyphs are cut out of Tj/TJ/'/" and replaced by a TJ displacement of the same advance, so the rest of the line keeps its exact position. Widths come from /Widths, /W//DW (composite fonts, embedded CMaps with codespace and CID ranges), Type 3 font matrices, and approximations for the standard 14. A glyph goes when it overlaps an area by more than a fifth of its size (or a point) both ways; zero-size text goes when its origin is inside;
• images: fully covered → removed; partly covered → a copy with the covered pixels cleared (8/16-bit and 1/2/4-bit images, image masks; Flate/LZW/RL/A85/AHx). Codecs PdfCraft can't re-encode (DCT, JPX, JBIG2, CCITT) are removed whole (fail-closed); inline images under an area are removed;
• vectors: covered paths are removed; partly covered paths and shadings are clipped so nothing paints inside the areas;
• form XObjects: rewritten recursively into new objects (pages sharing the original keep it);
• annotations whose rectangle overlaps (with their pop-ups), and form fields with a widget under a mark;
• the marks themselves, replaced by boxes in their fill colour (and overlay text) drawn into the page as a /PCMark /Redaction stream.

A verification pass re-reads each redacted page and fails the operation if any glyph or inline image is still under an area. Content that can't be decoded makes the operation fail rather than leave it unredacted.

Structure cleanup resolves named MCIDs and indirect content references. Form content references are updated to the cleaned copy; unchanged sibling descriptions remain.

A redacted page that inherits /Resources from the page tree gets them pinned (by reference; a direct inherited dictionary is made one shared object first) before it is rewritten. The parent's /Resources is then retired unless another page still inherits it, so it cannot keep a removed XObject reachable. Pages that aren't redacted are left untouched.

Remove hidden information / Sanitize

let found = sanitize::scan(&doc);                          // [(Hidden, count)] per category
sanitize::remove_hidden(&mut doc, &[Hidden::Comments])?;   // chosen categories
sanitize::sanitize(&mut doc)?;                             // all of them

Categories: metadata (/Info, XMP), file attachments, comments, form fields (flattened so the values stay visible), hidden text (render modes 3 and 7, or wholly off the page), hidden layers (content of off optional-content groups, then the groups), bookmarks, links/actions/JavaScript, and /PieceInfo private data. Both make the next save a full rewrite.

patterns finds phone numbers, e-mail addresses, credit card numbers (Luhn-checked), US Social Security numbers and dates for Search & Redact.

codes holds the redaction code sets (U.S. FOIA and U.S. Privacy Act exemptions): CodeSet::from_id("foia")?.overlay(&["(b)(6)"]) gives the overlay text for the picked codes. Custom code sets aren't supported yet.

Not yet: pattern locales, struct-tree/alt-text cleanup, metadata and hidden-information sanitising (M8.4), re-encoding of DCT images (they are removed instead).