The file extension APF is used by older versions of the Adobe Acrobat document file software. These files are used to add a digital signature to a PDF document. In this way, it can be determined later, for example, who has made which change to the document.
These profiles or certificates can be loaded under the security setting under 'Edit -> Protection' and are usually password protected. Also with the Acrobat Reader such files can be attached, for example for the writing of comments in pdf documents.
Newer versions of Acrobat use a different format for these profile files with the extension pfx or P12 (MacOS).
Most often resolving problems with opening APF files is very simple. Just install an appropriate program that supports such files. All of the listed programs support APF files, but may vary in offered function and purpose. Some programs may be capable only of viewing contents of APF files or offer file conversion options, but may not be capable of editing such files.
It is possible that although a compatible program has been installed on user’s system, it is not used by the system to open it. This may happen because no default application was associated with this type of files. To associate APF files with given application, select "Open with" from drop-down menu (accessed by right-clicking on the file). Then select from the list the program or application you want to be used to open this type of file. If the Adobe Acrobat applications is not on the list, select "Browse" option in order to manually locate the directory where Adobe Acrobat has been installed.
Sometimes problems with opening APF files may not lie with the application itself, but can arise due to other causes, such as: