Signature Verification
Inspect signature fields and verify signed byte ranges.
Signature verification is exposed on PdfField for fields whose fieldType is Signature.
This verification checks whether the signature cryptographically matches the PDF bytes covered by /ByteRange. It does not validate certificate trust chains, trusted roots, CRLs, OCSP, or legal identity. In other words: it can tell you whether the signed bytes still match the signature, not whether you should trust the signer with your lunch money.
Inspect signatures
const doc = await PdfDocument.open("/path/to/signed.pdf");
for (let index = 0; index < doc.fieldCount; index++) {
const field = doc.getFieldAt(index);
if (field.fieldType !== "Signature") continue;
const info = field.getSignatureInfo();
if (!info.hasSignatureValue) continue;
console.log(field.fullName, info.signerName, info.signingDate);
}getSignatureInfo() returns:
interface PdfSignatureInfo {
hasSignatureValue: boolean;
filter?: string;
subFilter?: string;
type?: string;
signerName?: string;
reason?: string;
location?: string;
contactInfo?: string;
signingDate?: string;
byteRange?: number[];
}These are dictionary-level facts declared by the PDF signature field.
Verify byte-range integrity
const status = await field.verifySignature("/path/to/signed.pdf");Status values:
type PdfSignatureVerificationStatus =
| "CouldNotVerify"
| "Invalid"
| "ValidNoTrust";| Status | Meaning |
|---|---|
ValidNoTrust | The signature is cryptographically valid over the signed bytes. Certificate trust is not checked. |
Invalid | The signature does not match the signed bytes, or the CMS signature is invalid. |
CouldNotVerify | The signature could not be checked, for example missing byte range or malformed contents. |
Invalidis a real cryptographic failure, not just an untrusted certificate. Common causes are verifying a modified PDF, signing the wrong payload shape for your key/HSM/KMS, returning truncated signature bytes, or using an older signing artifact with a known RSA signature-size bug. If you sign with RSA-2048 or larger, use PoDoFo 0.0.16 or newer.
Full example
import { PdfDocument } from "@doko/react-native-pdf-editor";
async function readSignatures(path: string) {
const doc = await PdfDocument.open(path);
const signatures = [];
for (let index = 0; index < doc.fieldCount; index++) {
const field = doc.getFieldAt(index);
if (field.fieldType !== "Signature") continue;
const info = field.getSignatureInfo();
if (!info.hasSignatureValue) continue;
const status = await field.verifySignature(path);
signatures.push({
fieldName: field.fullName,
status,
...info,
});
}
return signatures;
}Trust validation is separate
To make a trust decision, your app still needs policy-specific validation:
- build and validate the certificate chain
- check trusted roots
- check certificate validity time
- check key usage / extended key usage
- check revocation through CRL or OCSP
- apply your business rules
PoDoFo exposes useful signing and parsing primitives, but it does not decide who your app should trust. That decision belongs to your product and security model.