I imported an stl file and it won't allow me to make any changes to the model. Help?
Import the STL as a solid body, not as a graphics body.
2016 SOLIDWORKS Help - STL and VRML Import Options
stl doesn't have Solid Geometry - download iges, stp, .......
As John indicated, another format is preferable to STL. However, if STL is all you have, or can't get another format, you may have some other options.
If you have SolidWorks Premium or Pro, you might be able to use Scanto3D to convert the STL to surfaces and solids.
If the STL has a small number of triangles, like 15,000 you could choose the Solid Body in the STL import options, if the STL encloses a volume. Otherwise, choosing Surface Body, which would import slightly more than 15,000.
Choosing Graphics Body will import millions of triangle, but its only useful as a visual reference.
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