fitted french doors, wont shut

There can be a fair bit in the glazing. This in turn can bow the frame out of alignment.

Start to check and level one side and use a long straight edge against the frame, and check for any daylight. Adjust according at the fixing points, by removing or adding suitably sized packers. If a fixing isn't used behind a fixing point it can distort the frame whilst the fixing is fastened.

Once door has been set, check the glass in the door. Fitters use the 'toe and healing' principle to align the door panel by inserting glazing backers at one one corner and the opposite corner.

This video show the principal.