Don’t know how to find offline help.
On the download page each version of LibreOffice is indicated inside of a frame. Inside that frame there are several clickable text items to choose things like Operating System, Translated User Interface and “Help for offline use: [language] (Torrent, Info)”.
Click on the last one, but be sure it corresponds to your version of LO.
As to @sveinki correct answer, I believe he is referring to here.
https://documentation.libreoffice.org/en/english-documentation/
