With Nitro Pro, you can add people to your Trusted Contacts by importing their public key certificate manually, or you can share your public key and their public key at the same time with the Request Contacts feature. You need to have the public key of a contact in Trusted Contacts to be able to validate any PDF files they have digitally signed.

A Digital ID is a security pass that allows you to create a digital identity, or to view a document that has been encrypted to prevent unauthorized access. You can create different Digital IDs for different tasks. For example, you can have a digital ID for opening accounting documents, and another one to open technical reports.

Digital signatures are like paper-based signatures, but better because they include encrypted information so you can verify their authenticity. You can digitally sign a document to securely record the identity of the author, and to verify the content has not changed. Digital signatures in a PDF document can show text, or an image such as a photo or an image of your handwritten signature.

A digital signature is much more powerful than a traditional paper-based signature. They provide you with a way to show a person signed a particular document at a particular time and helps to ensure that the document content has not been tampered with after it was signed. Additionally, the document version history shows recipients when a document was signed, and when changes were made. This revision history is encrypted and stored inside the PDF, and can be viewed in the Signatures pane.

Digital timestamps mark a PDF signature with the time and date as proof of integrity. A timestamp shows that the contents of the document existed at a point in time, and are unchanged. For added security, digital signatures can include a timestamp from an independent, trusted authority. Nitro Pro is able to utilize a timestamp server to help ensure that the timestamp is precise and secure, since the system clock could be modified by a user.

A digital ID is much like paper-based identification such as a passport. It can prove who you are and give you special rights to do particular things. In Nitro Pro, your digital ID can let you make your PDF files tamper-proof, as well as give you special access to files from users who have approved your digital ID. When you secure a document, you can change access and usage rights on a user-by-user basis.

You can customize digital signatures to make information you want to share visible, and also to display your physical signature, a corporate logo, or some other graphic you want to appear alongside your signature. You can edit the appearance of your signature at the time of signing a document, or at any time.

As the author of a document, when you certify it, you attest to its contents and control what (if anything) can be done to it while retaining its certified status. If changes occur to the document that you have not permitted, then the document is invalidated and the certification is revoked.

Signatures are validated when a document is opened, and then automatically re-validated when anyone changes the document. The Signatures pane lists all signatures in the PDF document, shows their validity status, and provides a summary of each signature.