🚀 go-pugleaf

Since I don't have Inside Mac or any source code here, this explanation is going
 to be a little vague, but here goes...

The method of attaching an icon to a document is simular to the method of
attaching an icon to a program.  First decide the file type id you are going
to use for your documents, like 'WORD' for MacWrite documents.  Then in your
program you need to call the toolbox after you create your document to attach
this as the file type and your program id as the owner.  Now go into ResEdit
and add three new resources to your program, a new bundle, a new FREF and 
the ICN# you want to use.  These should be simular to the ones you created
for your program icon, the FREF specifying the file id, and the bundle 
specifying the FREF and the attached ICN#.  Now just set the bundle bit and
rebuild the desktop and the finder should give the documents the proper icon.

Brian Rauchfuss