I am trying to open/edit Photoshop Files from Sharepoint Document Library. I
could complete

the first two steps . But I am not able to do the third step. Please help

Creating a document template file, which in effect adds a DocumentTemplate to
the Onet.xml file of the site definition

Adding a Mapping element to DocIcon.xml for a file type icon and for
identification of the control to use to open the file

Creating a DLL that provides the necessary functions for creating or editing
documents in the application.