Their download link does not work.

Try these:

https://github.com/corkami/pics

svg: https://github.com/corkami/pics/blob/master/binary/pe101/pe1...

png: https://github.com/corkami/pics/blob/master/binary/pe101/pe1...

pdf: https://github.com/corkami/pics/blob/master/binary/pe101/pe1...

a general workup of assembler but also at the second subtitle,[PE Tutorials] a good treatment of how PE files, and PE loaders work

https://web.archive.org/web/20080714022022/http://win32assem...

supplemental:

https://github.com/JeremyWildsmith/PELoader

https://en.wikipedia.org/wiki/DLL_injection

https://en.wikipedia.org/wiki/Portable_Executable

this fellow has a git for a PE loader, there is supplemental knowledge articles linked in my other comment in this thread.

https://github.com/JeremyWildsmith/PELoader#readme