You received a signed contract, an invoice or an official letter as a PDF. Before you rely on it, two questions matter: is the signature a real digital signature or just an image, and has the document been changed since it was signed?
Two very different kinds of signature
- Digital signature: cryptographic data inside the PDF (PKCS#7 or CAdES) that ties the document to a signer's certificate. Any change after signing breaks it.
- Visual or electronic signature: an image of a handwritten signature placed on the page. It shows intent, but proves nothing about who placed it or whether the file changed.
Step by step
- Open the tool. Go to pdfmerger.io/verify-signature.
- Add the signed PDF.
- Click "Verify Signature".
- Read the report: digital signatures found, the signer name and signing date, ByteRange integrity, and whether the last page carries a visual signature image.
What ByteRange integrity tells you
A digital signature covers a list of byte ranges in the file. If those ranges cover the whole file, nothing was added after signing. If they don't, the document was modified after it was signed, for example with another signature, a comment or an edit, and you should look at what changed.
What this check does not do
It inspects the structure and contents of the signature, but it does not validate the signer's certificate chain against trusted certificate authorities. For that legal-grade validation, open the file in Adobe Acrobat Reader, which uses your system's trusted certificates.
Private by design
Signed contracts are exactly the documents you shouldn't upload to an unknown website. The check runs in your browser with pdf-lib, and the file never leaves your device.
Related tools
- Need to add your own signature? Sign PDF.
- Worried a PDF from an unknown sender is malicious? Scan it with the PDF Virus Scanner first.
Check a signature now: pdfmerger.io/verify-signature.