SaveAsReachable method

Rewrites the document as a single clean revision that keeps only the indirect objects reachable from the catalogue and the trailer /Info dictionary

PDFium first writes a non-incremental copy of the current in-memory document so the rewrite starts from canonical bytes

The object graph is then parsed and a document-wide reachability walk from the catalogue collects every surviving indirect object, including the page tree, page resources, fonts, images, form XObjects, AcroForm, structure tree, outlines, name trees, optional content, metadata, output intents and associated files

Objects left unreachable by incremental updates, page merges, or repaired saves are dropped, and the output is a single classic revision with no object streams and no cross-reference stream

Object numbers and generations are preserved, so every surviving cross-reference stays valid without renumbering; unreachable objects become free entries in the rebuilt classic cross-reference table

The rebuilt trailer carries /Root, /Info and /ID forward only when the referenced objects survived the sweep

• TPdfPruneReport reports the kept and pruned indirect object counts, the source and output byte sizes and a structured failure message
• Encrypted documents are rejected because a single-revision rewrite cannot honour the object numbers, byte ranges, and per-object keys that encryption depends on
• Signed documents are rejected unless AllowSignedDocument is explicitly enabled because a full rewrite invalidates existing signature byte ranges
• The output is a complete rewrite, so it does not preserve prior incremental revisions or historical object generations beyond the kept objects

SaveAs, SaveAsRepaired, SaveAsNormalizedContent