To be able to sign your documents, you need to pass the registration process in the ZealiD App successfully.
ZealiD Qualified Electronic Signatures are added to a document by scanning QR codes with the ZealiD mobile App.
How to sign a document in Evidos?
How to sign a document in Adobe Acrobat Sign?
How to sign a document in DocuSign?
How to sign a document in Foxit?