Unable to extrude (cut) sketch face on imported mesh?

[jklimekRYTHZ]

I've imported a STL file (https://www.thingiverse.com/thing:4693183) and I'm trying to cut ventilation holes onto the top of the enclosure and the sides.

However, when I create a sketch on the top piece of the case and try to extrude (cut), I don't have that option.

Can anybody explain what I'm doing wrong?

I've attached my F3D file with the sketch created that I can't extrude/cut.  (Here is a link to the same design if that's easier?  https://a360.co/434p78L)

[jeff_strater · Accepted solution]

Hmm... it works for me.  Are you sure you are using Solid Extrude (blue icon), and going in the right direction?

[jklimekRYTHZ]

Hah!  I've tried it several times and when I made my example it works apparently.  Sorry for the trouble and thanks for the help!