So I am applying for a postdoc position and I happen to be working on a problem that is quite closely related to PI's interests. I don't just mean that we share the same field/subfield (which we do anyway) but rather the problem that I worked out is an advancement of what he (and some other people) is doing. This makes my case particularly strong since he wants to work on related questions.
Now, I recently uploaded a preprint of my this work and I was thinking that if I highlight this paper in the cover letter for the application, my application would stand out. Including a direct link to the preprint sounds like an option to me. However, I have never seen a cover letter with links to papers. Is this possible and acceptable?