I’ve been using the More Purple More Better (MPMB) character sheet in combination with Adobe Reader on my Windows pc. It isn’t exactly an application replacing your char sheet, but an interactive PDF file reliant on JavaScript. It has a common recognizable layout, and is filled to the brim with macros and generation tools - you’ll be able to whip up a char sheet in no time once you get the hang of it.
Out of the box it only has PHB content, but you can add additional scripts containing every bit of official content for 5e. It isn’t very hard to find, either, /r/MPMB for example.
Sounds like there’s a step missing somewhere.
You should probably use a downloader such as NZBget or SABnzbd to download the whole collection of .rar archives (if it’s archived at all) and .par2 files associated with it. You’d download an NZB file for which content you wish to have, which is a simple file that tells the downloader how to download everything, fix them up when necessary and to repair the files, to finally extract a usable file for you.
That output is something Readarr should be able to use, like an epub.