Catia Users

You need to have a step or iges file to open in most CAD programs. Or, you need to post or write a step or iges file for others to open in most CAD systems. The biggest down side to GrabCAD is that most people do not post a step file. They post native CAD data that can only be read by people that use that particular CAD software. For example: Many people upload SolidWorks files. I do not have SolidWorks or access to SolidWorks, therefore, can not open those files. I use Catia.

you can ask the owner to upload step file of that project

Yes, for sure. I have done that.

If you want to convert any CAD file, the best way is to use a software program, for example: CrossManager (https://en.freedownloadmanager.org/Windows-PC/CrossManager.html).