Kirill,

I have an essay at my web site called A Mathematica Style that among other things gives an overview of using Workbench to create documentation. Documentation would usually be part of a larger entity called a Mathematica Application, which might include various combinations of notebooks, packages, style sheets. palettes and documentation. The essay discusses how to lay this all out. Mathematica Applications are quite a standard part of Mathematica and the Wolfram Language and a good way to organize work.

Workbench comes with Premier service but there may be other ways to obtain it. You would have to contact Support.

Recent versions of Mathematica, V10+, require Workbench 3. This is not even in formal beta testing, but it usually can be obtained by contacting Wolfram. I use it constantly for documentation and it works perfectly well. I don't know what Wolfram's long term plans are for documentation. I just cross my fingers and hope that whatever it is, it will maintain compatibility with present paclet documentation.

Documentation cab be created using Wolfram Workbench. See the Worbench documentation on how to do it: http://reference.wolfram.com/workbench/ It's under Mathematica Development User Guide -> Tasks -> Documentation.

Workbench 2 may not be fully compatible with recent versions of Mathematica (I'm not sure), so you may need to request a beta from Wolfram Support ...

I haven't used these tools in a while so I'm not sure.

Can we do it without the Workbench? In principle, yes.

I found two packages on http://packagedata.net/ that claim to do it. ApplicationMaker used to work, but I think it's a bit outdated now and may require fixes. There's a new 'userhelp' package which was posted a few days ago. I never tried it.