PDF Signature Presence Checker

Overview

Detect whether a PDF file contains embedded digital-signature dictionaries, entirely in your browser. The tool scans the raw file bytes for the markers PDF signatures require - /ByteRange, /Type /Sig, /SubFilter and /Contents - and reports exactly what it found, including the ByteRange byte spans and the signature handler values. It is a presence detector, not a validator, and the page says so in those words.

How It Works

Select a PDF to scan. The page reports how many /ByteRange markers and /Type /Sig dictionaries it found, whether a /Contents blob is present, the parsed byte-span array of the first signature, and the distinct /SubFilter and /Filter values such as adbe.pkcs7.detached or Adobe.PPKLite - the real values from your file, not assumed ones. A prominent panel above the result states what the tool does not do, and when signatures are found a second notice repeats it beside the details. The result appears immediately after the file is read - there is no server round trip, and the file is decoded locally into memory for the scan.

Step-by-Step Usage Guide

1. Select the PDF file to scan.
2. Read the verdict: signature dictionaries detected, or none found in the raw bytes.
3. Check the details: ByteRange count, parsed byte spans, SubFilter and Filter values.
4. For legal verification, confirm with a full cryptographic validator such as Adobe Acrobat.

Technical Specifications & Standards

What the check actually does deserves a precise description, because the difference between detecting and verifying a signature is a security boundary. The tool decodes the file bytes one-to-one as Latin-1 text and counts marker occurrences: /ByteRange, the PDF keyword that defines which byte spans of the file the signature's hash covers, with its four-number array parsed out where it is well-formed; /Type /Sig, the signature dictionary marker; /SubFilter, which names the signature encoding such as adbe.pkcs7.detached; /Filter, which names the signature handler such as Adobe.PPKLite; and /Contents, the placeholder that holds the cryptographic message. What it does not do: parse the PKCS#7/CMS cryptographic container, verify the certificate chain against trusted authorities, check certificate expiry or revocation, or confirm that the document bytes covered by /ByteRange are unmodified. Two scan-level caveats also apply: signatures stored inside compressed object streams are invisible to a text-level scan, and a marker string in unusual content can produce a false positive. For anything legally consequential - a contract, a filing - verify with Adobe Acrobat or your national validated tool, which perform the full chain and integrity checks this page does not. A detected signature is not a verified signature.

Targeted Use Cases

• Quickly checking whether a downloaded form was digitally signed at all.
• Triageing a batch of PDFs to find which ones carry signatures before deeper validation.
• Learning how PDF signatures are stored by seeing the markers and their values in context.
• Confirming a document you signed yourself actually contains signature data.

Notes & Gotchas

• Treat a positive result as 'signature structures present', not 'signature valid'.
• Use Acrobat or a national validation service for contracts and filings.
• Remember the file is inspected locally - nothing is uploaded, so sensitive documents stay on your device.
• A negative result means nothing in the raw bytes; it is not absolute proof a signed copy never existed.

Frequently Asked Questions