>Edward!
>Is there any way to determine from what position and what text has been selected in MODIFY FILE IN WINDOW. I can see a way to drag the text, but I don't know from what position and what length it can be assigned to SUBSTR() that part.

The simplest way is to use Copy/Cut/Paste. If it's not sufficient, then you should use Editbox (i.e. Editbox.Value=FGETS(....) or FREAD(...)) with SelLength,Selstart properites.