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What a digital signature actually proves

A digital signature is math, not a picture of handwriting. It proves exactly three things, and nothing past them.

What it proves

1. The signed bytes have not changed since signing.
2. The signature was made with a specific private key.
3. The certificate attached to that key names an identity.

What it does not prove

It does not prove the named identity is truthful. Anyone can make a certificate that says anything; what matters is who issued it and whether you trust the issuer. It does not prove the document's claims are true. It does not prove the signer was authorized to sign.

Pages and coverage

A signature covers a byte range, and in multi-signature documents different signatures can cover different revisions. A report should tell you which pages fall under a signature and which do not.

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DocVerdict reads the signature, verifies it, names the signer from the certificate, and reports whether anything was added after signing.