The objective of the project is the study and implementation of a mechanism for advanced electronic signature for PDF documents (PAdES). The project is comprised of an API for the signing of PDF documents based on the formats mentioned in the standard TS 102778 from ETSI (European Telecommunications Standards Institute). The API must allow the generation and verification of electronic signatures for the following profiles: PAdES Basic, PAdES Enhanced and PAdES Long Term. The API will use digital certificates and keys stored in PKCS#12 containers or in cryptographic tokens (PKCS#11). The programming language which should be used is C#.