# PDF Signature Checker Guide

Inspect the digital signatures embedded in a PDF.

- Tool: https://ilham.dev/tools/pdf-signature-checker/
- Guide URL: https://ilham.dev/guides/pdf-signature-checker/
- Tool guides index: https://ilham.dev/guides/tools/
- Broader guide: Working With PDFs (https://ilham.dev/guides/working-with-pdfs/)

## What it does

Read a PDF and report the signatures it contains: who signed, when, and whether the byte range each signature covers still matches the file. It walks the PDF structure directly, with no upload and no external library.

## Use the tool

Open https://ilham.dev/tools/pdf-signature-checker/, add the input the tool asks for, run it, and check the output before using it elsewhere.

## Input and output

- Input: text.
- Output: text.
- Category: Crypto.

## Privacy and processing
Processing happens locally in your browser. This tool does not upload the input to ilham.dev.

## Questions

### Does this prove the signer's identity?

No. It checks that the signature covers the current bytes and reports the certificate details. Whether to trust that certificate is a separate judgement, and this tool does not make it for you.

### Why is a signature reported as invalid?

Usually because the file was changed after it was signed, which is the check doing its job. It can also happen with signature formats the reader does not recognise.