This multi-part tutorial will present several ways in which you can add functionality to closed source Windows executables through DLLs, PE header modification, and good old assembly code. Adding code to existing code caves, modifying PE headers to create code caves and/or importing DLL functions, adding backdoors to programs, and adding plugin support to closed-source programs are all covered.
You can download it from the following link: https://packetstormsecurity.com/files/download/49738/win_mod.zip
Source: https://packetstormsecurity.com/files/49738/win_mod.zip.html