Check PDF signatures

How it works

When you open a PDF with signatures, a line appears at the top stating how many it has; one click opens this tool (you can also search for it as “Check signatures”). For each signature, six blocks are shown: whether the document changed since then, who the certificate says signed, whether the certificate is trusted, whether it was revoked, when it was signed, and the long-term validation level. Each check appears with its status written out (passed, failed, or not checked) and an icon, never just a color.

The tool gives no overall verdict and does not claim that a signature is “trusted”, “qualified”, or “certified”. Judging trust requires a list of trusted certificates, and this site does not include one: as long as none is provided, the panel states that no trust list was provided and displays only what the file claims. The signer always appears as “claimed”: it is what the certificate says, not an identification of the person.

Two optional actions create a new copy of the file: adding long-term validation data and adding a document time stamp. Neither is done on its own. If anything must leave your browser (the revocation check to the issuing authority, where that service exists, or the hash for the time stamp), you are asked beforehand and can change your answer in Settings; the file is never sent. You can also download a JSON report of the check.

What is not preserved, and limits

• This tool checks the integrity and structure of the signatures and displays what the file claims. It does not state whether a signature has legal validity or whether the signer is who they claim to be: that depends on applicable law and on who issued the certificate.
• Without a list of trusted certificates, trust is not judged. This site does not include any list or decide who is trustworthy. You can import certificates (.cer, .crt, .pem) for that session: they stay in the device's memory and are lost when closing, and having a certificate on your list means only that.
• The full certificate-chain validation rules (RFC 5280) are only partially implemented: the signature on each link, CA constraints, and path length are checked, but name constraints and policies are not, and the panel marks them as not checked. For formal validation or for an EU qualified signature, a dedicated validator is also required.
• The page is not rendered. A change added after signing that the analysis classifies as permitted (filling a field, adding another signature, or adding validation data) could still alter what you see; the panel warns of this, and lists changes it cannot classify.
• Revocation is checked using the data already carried in the file. Online queries are optional, exist only on site builds with that service enabled, are prompted before each send, and the issuing authority gets to learn the certificate's serial number (see Privacy).
• The time claimed by the signer is shown as claimed. Only a verified time stamp provides a time backed by a third party, and without a trust list it is also not known whose it is.
• Adding validation data or a document time stamp creates a new copy: the open file and your original are untouched. Nothing is done without you clicking the button, and the copy has no more legal standing than the original signature had.
• Everything is calculated in your device's memory and the file is not sent anywhere. Very large files may take time or fail, especially on mobile devices. To keep a hostile file from freezing your browser, the tool examines at most 50 signatures per file, does not open compressed data that expands to more than 64 MB, and tells you what it did not examine. You can cancel the check, and also the two actions that create a copy (validation data and time stamp).
• Results have been checked against independent tools (openssl, poppler's pdfsig, and pikepdf) on test files. They have not been compared against Adobe Acrobat or official EU validators, and testing was done only in Chromium (not in Firefox or Safari, nor with touchscreens or screen readers). The line “This file has N signatures” counts the signature dictionaries it finds, which includes document time stamps.