I said I could not help directly, because this is just not my bag.
However, intrigued by your keenness to get this into Shapr3D, I did download the File and open it in FreeCAD. I know less about FreeCAD than any other software on any of my Devices.
I exported the File as STEP and true to your experience it failed, in that it appeared to have spawned an Empty File.
Seeing the Model in all its glory in FreeCAD I tried to Export to PDF, with success but frankly the quality was poor the great detail of the model lost in the thickened lines. The beautiful Handle Grip was a large splodge of darkness.
Never one to give up and roll over another attempt was made to create the STEP File and this time, after the passage of several minutes, it actually contained something.
I am giving the full state of progress in case you try copying this process.
Waiting for it to load on the iPad was an edge of the seat job.
The Shapr3D loading indicator almost immediately expanded from 12 o’ clock to 1 o’ clock.
Then it hung and hung some more, just as I was about to do something about it [not sure what that would have been] the indicator progressed to about 4 o’ clock and hung again.
Again a long wait and it progressed on to just past 6 o’ clock. Another wait period.
Suddenly the indicator retracted back to 12 o’ clock and it was beginning to strain my patience, but with time invested I decided to wait.
The reward was, you will have guessed, after a further wait the indicator behaved as previously described but fortunately a little quicker. That is not to say the iPad usual standard. On getting past the 6 o’ clock position it carried on in stages to complete the clock circuit.
Seeing the Model in Shapr3D was an absolute delight, exactly as expected so crisp and clear.
This ScreenShot was created using Shapr3D Image capture feature.
Colt Test.shapr is 109.8MB if it is needed I am happy to send it.
In the UK a ‘printed’ version of this carried in any public area would be an offence, I would not like to see any bad outcome for anyone.