You could put some code in the Onchange event for the Rich Text Lite field. That could would look in the field, detect any attachment and warn teh user (or even delete the attachment) if the extension is incorrect.
What I would do, however, is to use the OpenFileDialog method of the NotesUIWorkspace class. There you can filter so only PDF files are being displayed. It won't stop a user from changing the filter and selecting another type of file, but you can check the return value and ignore any files without the .pdf extension.
This method will also not prevent the user form manually attaching a file in the field. You can make that harder by not displaying the field delimiters on the rich text field.
In teh long run, there is only so much you can do, if users keep attaching the wrong type of files by bypassing the restrictions you have setup, it is a management issue, and their managers need to stop it.
Attach only .pdf doc LS (Gabrielle R Cou... 19.Dec.12)
Feedback response number WEBB935LCR created by Karl-Henry Martinsson on 12/19/2012
. . Onchange event (Karl-Henry Mart... 19.Dec.12)
. . . . DialogBox but.. (Gabrielle R Cou... 19.Dec.12)
. . . . . . Left$ perhaps? (Karl-Henry Mart... 20.Dec.12)
. . . . . . . . Thanks you (Gabrielle R Cou... 20.Dec.12)
. . . . . . . . . . Expanded class (Karl-Henry Mart... 21.Dec.12)