Documentation

Maybe you could have a look at a combinatino Framemaker, RoboHelp, Captivate which are all part of the Techinical Communication Suite?

Adobe Technical Communication Suite (July 2017 release)

I very much doubt you could legitimately call Captivate a documentation tool.  It does output MS Word documents in the form of Handouts that are reminiscent of PowerPoint handout docs, but the options to format those documents are extremely limited.

I have used UPK in the past for projects and I know what you mean about developing documentation output as well as elearning output from the same source files.  But the downside of that tool (in my opinion) turned out to be that by trying to cover too many different outputs it limited what you could do in each one.  We ended up using Captivate on that same project to develop the e-learning and had to graft the Cp output into the final solution in order to satisfy the client's requirements.

I think you will find Captivate is much more a dedicated e-learning authoring tool and that's what it does best.