PSPad from 4.3.3 version supports plugins for file load/save manipulation. Plugins are stored in the .\Plugins\FileType folder as dynamic link library (.dll) files. The name of each dll indicated it's functions are called when loaded and/or saving a file with a matching file extension. i.e. pdb.dll handles files with the pdb (*.pdb) extention
Each library has simple interface, exports there functions:
Maximal size is limited to 5,000,000 bytes. If some error occurs in dll (function missing, function returns false), PSPad internal file handling is used. PSPad internally checks the PSPad version Plugin is designed for. A error is raised if version is less then current PSPad interface version and PSPad uses internal file handling.
Note: Current interface version is 1.