LilyPondTool includes an embedded PDF viewer, that is, you don't need a separate viewer (like Adobe Reader) to view the score. This PDF viewer is based on the GPL version of the JPedal PDF library. The limitations in this library can cause that in some very rare cases not everything is displayed exactly the same as in the official Adobe viewer, so we call in just preview. This viewer also doesn't support the printing of the score. For that purpose you must use an external viewer. (Which you should have anyway somewhere on your computer.)