Verify a signed PDF
Check whether a document sealed with OpenSigner has been changed since it was signed.
Processed locally. Your document is opened in this browser's memory and is never transmitted over the internet. You can even go offline now.
Drop any signed PDF here to verify integrity.
The hash is computed on this device with WebCrypto.
How the seal works
When a PDF is finalized, OpenSigner writes it with a fixed-length slot in its metadata, computes SHA-256 over every byte with that slot set to zeros, and writes the result into the slot without moving anything. Verification repeats the calculation. Any change anywhere in the file, even one byte, produces a different hash.
The seal shows whether a file is intact. On its own it does not prove who made it, because anyone could seal a new file. To confirm a document is the one that was signed, compare its seal with a copy the signer shared, or scan the certificate's QR code, which links to the original document's hash.