I am able to open large files and it works great, however I do not get line numbers even though that option is on by default. It does for xml files, but a text file with .xml extension does not.
Any ideas on how to get the line numbers or maybe the software is not meant to do that?
The Large File Editor does not display line numbers.
It does have the concept of lines, so you can move to a specific line using menu Edit->Go to... (Ctrl+G).
Depending on your PCs specification, you may be able to open larger files without invoking the Large File Editor, please see:
Opening Large XML Documents in Liquid XML Studio