For me I had to go through a few steps to get it to work – as a side note I did it with audio mp3 files not pdf or anything.
1. Right click the file and copy link
2. It should come up with a dialogue box that says “People in *domain* with the link can edit”. Click on that.
3. Uncheck the “Allow Editing”
4. Click apply then copy the link it gives you
5. Add “&download=1” to the end of it and then put that in a browser url address bar and hit enter.
6. It will then produce an expanded url and when I copied the expanded url it produced it was basically a direct download file for the audio. That worked fine for me.
Best of luck.