Is there a way to find the installed Libreoffice version number (e.g. 3.5.7) on Windows? I can't see a registry key or plaintext file with that information.
Look in control panel. On the far right their should be a version column. If you do not see that column you can add it by right clicking the column header and checking the version option. For example, currently in that column it shows version 18.104.22.168 for my installation of LibreOffice.
There is a version configuration file under the directory "C:\Program Files (x86)\LibreOffice 3.6\program" the file name is "version".