Both Windows and MacOS allow a user to launch an application by double-clicking (or "opening") a document associated with it. However, there is only one application that can be associated with any given "file type" (determined by the final extension on the file name) and applications have increasingly fought over the double-click rights to different extensions. This was particularly the case with extensions that would be naturally opened by a web browser.

RATS lets the operating system know that it can open .rprj (RATS Project File), .rpf (RATS Program File), .rat (RATS data file), .src (RATS procedure or "source" file) and .prg (older program files). However, the double-click associations are maintained by the operating system—as a general rule, an application will get the association if no other program already has it. At one point, the most recently installed application would take over the double-click association, which led to programs grabbing up every extension they could. So the operating system rules (for both Windows and Mac) changed to leave the association with the first installed. Because of this, if you have an older/different version of RATS already installed, the double-click association will remain with the previously installed software. Also, .rpf is now also an obscure extension for a type of game archive and some archive/unzip programs are now including it in their list of file type associations, so if even if you have never installed RATS, you might have a double-click problem with an .rpf file.

 

Our recommendation is that you get used to starting RATS through the application icon or shortcut, and then opening up a program file using the File menu operations (File>Recent Files is particularly helpful). However, if the double-click operation on the .rpf or .rprj is pointing to the wrong application, you can fix it as follows:

Windows
 

If there are two programs installed which claim double-click rights for a file type, the first one installed keeps it unless you override it. Unfortunately, if two are installed and you uninstall the first one, Windows doesn't automatically shift to the other, so you have to

 

1.Find an .rpf or .rprj file in Windows explorer

2.Right click and do Open with...

3.Choose Default Program.. and select the new version of RATS. This should set Windows so it opens the proper version of RATS from then on.

 

You would have to repeat this process with the other extensions if you think you might use them.

Macintosh
 

1.Find an .rpf or .rprj file in the Finder

2.Right (control) click on the file

3.Click on Get Info in the pop-up

4.Click Open With if the section isn't already expanded

5.Click the drop-down menu and select the most recent version of RATS

6.Click Change All...

7.Continue when the Finder asks you if you're sure

You would have to repeat this process with the other extensions if you think you might use them.

 

Copyright © 2026 Thomas A. Doan