Digital signatures

You can sign documents with digital signatures. It is possible to sign already signed documents without invalidating existing signatures. You can specify which fields to lock after signing. The library supports embedding timestamps in digital signatures.

Docotic.Pdf can read signature properties, check if the document was tampered with after signing, check if the signature certificate is revoked.

Articles

Check the articles about features of the library related to digital signatures.

• Sign PDF documents in C# and VB.NET
  Sign PDF documents, use handwritten signature images, lock PDF form fields with signature in C# and VB.NET using Docotic.Pdf library.

• Verify PDF signature in C# and VB.NET
  Read and verify digital signatures in PDF documents using Docotic.Pdf library.

Sample code

These sample codes illustrate different approaches to signing documents with digital signatures.

• Sign document
  Create digital signatures using different digest algorithms (SHA-1, SHA-256, SHA-384, SHA-512, RIPEMD-160) and different signature formats (adbe.pkcs7.detached, or ETSI.CAdES.detached).

• Sign an already signed PDF document
  Sign PDFs without invalidating signatures already applied to the file. It does not matter who and how signed the document before.

• Sign a PDF form by multiple people
  Get a PDF form sequentially signed by multiple people.

• Sign PDF document and embed a timestamp
  Get a timestamp from the specified Timestamp Authority and embed the timestamp into the signature.

• Signature fields
  Add regular and invisible signature fields to PDF documents.

• Sign signature field
  Sign a specific signature field that already exists in a PDF document.

• Sign signature field using custom style
  Provide custom labels or images. Specify if you want the signing date and the certificate Distinguished Name visible in the signed field.

• Sign signature field with lock
  Create and sign a signature field with lock. The signature field lock specifies which fields should be locked after the signing.

• Sign PDF documents using AWS KMS
  Use keys from AWS KMS to sign PDF documents.

• Sign PDF documents using Azure Key Vault
  Use keys from Azure Key Vault to sign PDF documents.

• Sign PDF documents using PKCS#11 drivers
  Sign PDFs with smart keys, USB tokens, and HSM devices.

• Read signature properties
  Read the name of the signer, the time of signing, the signer's contact info. Access the signing certificate embedded in the digital signature.

• Verify signature
  Check if the signed part of a PDF document was changed after signing, if a signature contains embedded OCSP and/or CRL data, if the signing certificate is revoked on a given date.