Summary Overview
How Filecheck detects internal database corruptions and runs automated repairs to heal damaged PDF structures.
What is PDF Structure?
A PDF is not just an image; it is a structured database containing streams of text, vectors, page boxes, and metadata dictionaries. These streams are indexed via a cross-reference table (xref).
If a file is saved incorrectly or interrupted during export (e.g. from design apps or web downloads), the internal database structure can become corrupted even if the file looks fine on a computer screen.
The Print Risk: PostScript Errors and Missing Graphics
Structural corruptions cause severe failures during prepress parsing:
- RIP Crashes: Damaged stream structures or broken xref tables will crash industrial RIP processors or cause PostScript errors.
- Missing Graphics: A corrupted content stream can cause some elements, images, or font glyphs to fail to draw, resulting in partially blank physical prints.
- Corrupted Pages: Pages may render as blank white sheets or cut off halfway down.
How Filecheck Diagnoses and Repairs PDFs
Filecheck acts as a proxy validator that tests and repairs document integrity:
- Structural Audit: We run the PDF through a parsing pass. Any syntax warning, malformed stream, or broken reference is recorded (
struct.structure_warnings). - Automated Repair Autofix: If warnings or errors are found, Filecheck runs the document through an automated repair utility (utilizing the
mutool cleanlibrary). - Database Rebuilding: The engine rebuilds the xref table, standardizes content streams, corrects outdated PDF version headers (
struct.pdf_version), and strips invalid object references. - Clean Pass: This outputs a reconstructed, structurally clean, standardized PDF that is guaranteed to process smoothly on any downstream prepress system.