I've searched for the copy and selection function but didn't found it.
After a search on the forum, I read that it wasn't there in the programme.
So my suggestion is: Why not a selection and copy paste function in tuxguitar?
It would be so much handier when you can copy pieces of a song to an other place in the same song.
I don't know how hard it is for programming, but I think it's an unmissable feature.
What tuxguitar don't support, is a copy/paste of a beat selection. but it have support for copy/paste measures.
Just go to "Measure" menu, and you'll found it.
Or, you can use the shortcuts ( if you didn't change them ) :
Copy = "Ctrl + c"
Paste = "Ctrl + v"