In the DayZ/Arma engine, file formats like .p3d (models) and .rvmat (materials) are not simply "zipped" or "encrypted" binaries. They are serialized data structures. Because the source code for the engine (Enfusion) is proprietary, converting a binary .p3d back into a editable project file (T-pose, selections, LODs) is without official tools.
Bohemia provides a modding kit (available via the DayZ Tools launcher on Steam) that includes several . You can study, edit, and recompile these freely. p3d debinarizer dayz free