Every Macintosh disk file has a "signature" which consists of two parts, a file type and a file creator. The creator indicates the application which will be invoked if you double-click on the file. The type may tell the creator application what to do with the file. Types and creators are 4-character strings. The file's icon is determined (at least by default) by its signature.
File signatures can be inspected and changed with shareware applications such as File Buddy, ResEdit, or others which can be found by searching for "signature" or "creator" at a shareware web site.
RasMol and other relevant type/creator signatures (case sensitive) are:
|RasMac application binary||APPL/RSML|
|PDB atomic coordinate file||TEXT/RSML|
|Simple text/Teach text document (plain text)||TEXT/ttxt|
|MS Word document||WDBN/MSWD|
|Plain text saved by MS Word||TEXT/MSWD|
|HTML document for web browsers||TEXT/MOSS|
Files obtained by ftp with Fetch default to whatever is specified in Fetch's Customize, Preferences, Downloading dialog, often set to TeachText or MS Word.
PDB files can be opened or loaded by RasMac regardless of whether their signature is TEXT/RSML (the proper one), TeachText, or MS Word plain text. However, if you want to drop them onto the RasMac icon to display them, they must be TEXT/RSML.
Scripts work most reliably if the original RasMac application icon has been dragged into the same folder as the script files. Scripts can be executed with a "script filename" command regardless of whether their signature is RSML/RSML (the proper one), TeachText, or MS Word plain text. However, if you want to execute them by dragging and dropping onto the RasMac icon, they must have the proper signature. Furthermore, the RasMac icon cannot be an alias, and even a copy of the original application file may not work.