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About this tool
Inspect local PDF signature dictionaries, validate bounded ByteRange coverage, and hash the exact signed bytes without claiming certificate or CMS trust.
PDF Digital Signature Validator inspects the signature dictionaries inside a local PDF and checks that each /ByteRange actually covers the file the way a signature requires — starting at offset zero, in ordered non-overlapping pairs, leaving exactly one gap that lines up with the /Contents hex string. It then computes a SHA-256 digest of precisely the bytes ByteRange selects, so you can fingerprint the signed revision. It is a structural check only: it never claims the CMS signature, signer identity, certificate chain or timestamp is trustworthy.
Open PDF Digital Signature Validator on AltFTool — it loads instantly in your browser.
Press 'Choose a PDF' and pick a local .pdf of at most 20 MB; the file stays in the tab, is never uploaded, and no pages are rendered.
Press 'Inspect structure' to walk up to 12 signature dictionaries, checking each /ByteRange starts at offset zero, holds ordered non-overlapping pairs and leaves one gap on the /Contents string.
Read the Candidates, Range-consistent, Issues and 'Prior revisions' tiles with the SHA-256 signed-range digest, then press 'Export privacy-safe report' for pdf-signature-structure-report.json.
It confirms the single ByteRange gap starts and ends exactly on the /Contents string and its delimiters, the classic place a forged range hides.
Each signature reports whether its covered range reaches the current end of file and how many trailing bytes follow it.
Every result ships with explicit limitations, so a range-consistent verdict is never mistaken for cryptographic or PKI validation.
No. It validates ByteRange structure and hashes the signed bytes; it does not parse the CMS/PKCS#7 blob in /Contents, check the certificate chain, revocation status, or timestamp authority. For legal or evidentiary reliance, verify in a full PKI validator and consult the relying party's requirements.
It must be an array of exactly 4 non-negative integers — two offset-length pairs — with the first offset equal to zero, every length greater than zero, the pairs ordered and non-overlapping, neither extending past the end of the file, and the single gap between them matching the /Contents string exactly. The parser will read arrays with up to 32 integers before it separately reports them as malformed, but any array longer than 4 integers leaves more than one gap and so is always flagged invalid — 4 integers is the only length that can pass.
Up to 20 MB per file, with the first 12 candidate signature dictionaries inspected and a total hashing budget of 64 MB across their signed ranges. Files or signature counts beyond those bounds are reported as truncated rather than silently skipped.
It fingerprints exactly the bytes that ByteRange selects, letting you prove two copies of a document cover identical signed content. It is not the message digest authenticated inside /Contents, so matching it does not by itself verify the signature.