Bibledit can import existing USFM files.
In the menu choose File / Project / Import.
Select the directory that contains the existing USFM files.
In most cases it is enough to then click OK.
The books will be imported.
See also: Import, Import text dialog.
Some standard texts have been provided by users. These are listed below.
UBS Greek Text. Comment: This server is in Jakarta, and extremely slow if you are not on that side of the globe. For use in Bibledit, I would recommend using the wonderful SIL Gentium font for the text display font.