There are two ways, at least, to control the application that opens a file. Simplest of these is to load the app. first, and then open the file from within the app. If app. and file are compatible, that's the end of the story.
The second is to specify—file by file if need be, but sometimes it is possible to do so globally—what app. will open what file. There are apps that arrange this for you. For example, Internet CP allows you to do so for your downloads. MacLink Plus in OS 8.1 enables much the same, and more.
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