Would anyone know how to convert .p3d file into .max / .fbx /.obj ? I’ve been searching for a while now without any results 
20 sec on google told me .p3d is from peak 3d software, presumable you could download it and the export it to whatever format you need it in.
i know arma 3 uses .p3d for some stuff
i’m going to put in the same disclaimer i put in for all these types of requests.
if you owned the file in question A: you would have the software that built it and could just export it or B: you would have the source art file that would more than likely be in the format you want.
Requests like this are often from people wanting to modify/use other peoples work, hence why they need to convert from a non standard format.