I'm trying a do mods and skin for PPD but i don't know how to do it, can someone help me with that?

You should ask this in flowscript forum. (If there is someone)

Maybe this is useful

http://projectdxxx.me/forum/board/id/3PPD=Project -Project Dxxx- フォーラ
(This link is different from the one on forum, it contain some tutorial about it {I think}) (note: open it on incognito tab otherwise you will be directed to another link)

I think it has something related to flowscript

Edit: nvm the link you can just change the language to Japan and go to the flowscript forum.