Look for the "For Each sheet in dwgs" line; comment it out and the corresponding "Next". Add a variable named sheet that refers to the current drawing sheet. Keep the rest of the code.
Code:
'For Each sheet in dwgs
Dim sheet As Drawings.DrawingSheet = workPart.DrawingSheets.CurrentDrawingSheet
.
.
.
'Next
Also, you may be interested in the code found here: