.pls files are a type of playlist. This playlist is a text document with the following format:
[playlist] NumberOfEntries=4 File1=/fs/My Music/Eloy/02 Journey into 1358.mp3 File2=http://some.website.com/music.mp3 File3=//NETWORKCOMPUTER/Videoclips/A12345.mp4 Title3=A Short Videoclip File4=any url to file
The VLC Mediaplayer requires the parameter in dark red. The parameter "Title(n)" is optional, but if presented with it, VLC will display the title in its Titlebar, and in case of video material the title will be briefly displayed on the screen at the beginning. The tile may not be displayed if a non-Latin characterset is used, eg., contains diacritical signs like ñ, é, ö, etc.
If an existing playlist does not work, check that it has the "NumberOfEntries" parameter at the beginning (some media players do not require it). Also make sure that the file is saved as an ANSI-text file and that the last line is finished off with a line break.