How to convert files from .SLDPRT or STL to .stp or igs?

there is a free software online called OnShape this https://www.onshape.com/ this software can open all of these files and will allow you to save them as in IGS fille which i believe you should be able to open without any extra licences in CATIA.

Onshape requires you to register with you email and you get i think 100MB free offline storage.

Also these 3D models they are on step, you can open them in Solidworks. without problems.
if it usefull just let us know.
Thanks,

Have a good day,

Use GrabCAD Workbench. Upload your sldprt file to workbench then you can right click on the uploaded file and select "download as". You can download the file in the format of STEP, IGES, STL, Parasolid, ACIS, JT, or VRML.

If your still struggling I'd advise you to check out my tutorial for converting files in Workbench
How to convert CAD files in Workbench

Old thread, but updated info may help for those seeking similar info.

I would say here is there main to go place for this question.
On GrabCAD there are many people always willing to help or to offer it as a service.
How to convert CAD files in Workbench

FreeCAD is a good free alternative with loads of available info online and a strong community.
https://forum.freecadweb.org/viewtopic.php?style=10&t=36063

You can also try different websites specialized on converting/exporting files.
You can also try:
https://www.cadmesh.com/
https://www.convertcadfiles.com/

Good luck!

Hi friend, good morning, I am attaching you a link, where you can find many Quadcopter assembly models, in 3D in step, and you can check them, they are in this page grabcad.com, the link is:
https://www.google.com.mx/search?q=Quadcopter+Assembly+3d+model+in+step&hl=es-419&gbv=2&tbm=isch&oq=Quadcopter+Assembly+3d+model+in+step&gs_l=img.3...7655.15726.0.15991.39.2.1.36.0.0.208.414.2-2.2.0....0...1ac.1.34.img..38.1.208.VCEXQGhLNI8