PAdES (PDF Advanced Electronic Signature) is a PDF-based signature format defined in ETSI 102 778 (1-6). PDF allows the signature to be embedded in the document itself rather than being created as separate data. The signature obtained by signing the PDF content is added to the Signature Dictionary field, which is reserved for signature in the PDF.

It is fact that only PDF content can be signed with PAdES; however, PDF content can also be signed outside of PAdES with CAdES and XAdES. The advantage of signing the PDF with PAdES is that the file created as a result of the signature remains in PDF, can be viewed by PDF viewers and the signature can be verified.

As stated in ETSI TS 103 172, the PAdES signature types are subdivided according to the validity period and the data it contains. These are B-Level, T-Level, LT-Level and LTA-Level. PAdES B-Level, PAdES LT-Level, PAdES LTA-Level, P4 PAdES LT-Level ve P4 PAdES LTA-Level are widely used.