Sign a digital contract as PDF: how to do it safely

Three types of digital signatures

There are three levels of electronic signatures (per eIDAS regulation in the EU). SES (Simple Electronic Signature): an image of a signature or typed name. Legally valid for many contracts but low evidentiary value. AES (Advanced Electronic Signature): linked to the signer via certificate or verification software (e.g. Adobe Sign Level 2). Better protected. QES (Qualified Electronic Signature): the highest level. Legally equivalent to a handwritten signature in all EU countries. Requires a certified smartcard or eID (e.g. German nPA or Belgian eID).

Simple signing with PDFrust

Upload the contract PDF to the Sign tool on PDFrust. Upload a transparent PNG image of your signature or draw it directly in the app. Position the signature in the correct location (typically at the bottom of the last page next to your name). Download the signed contract. This is an SES — suitable for most everyday contracts.

When a higher signature class is needed

Use an AES or QES for: employment contracts and termination letters, mortgage deeds and purchase agreements, medical consent forms, and international trade contracts. For these cases use Adobe Sign, DocuSign, SignNow or a national qualified eID signature service.

Flatten after signing

After signing it is recommended to flatten the document so the signature cannot be removed as a separate layer. Use the Flatten tool after signing. Save the flattened document as the definitive version.

Archiving and proof

Always keep the final signed PDF together with an email confirmation from the counterparty. Save with timestamp in the file name: "2026-07-25_Contract_Partyname_signed.pdf". For higher evidentiary value: have a QES provider add a timestamp token — this irrefutably proves when the document was signed.

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