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jet3004 said:
How do I do it? I am puzzled?

If you know what kind of file it is supposed to be, you can add the suffix for that program (i.e. ".qxt" for a Quark document, ".doc" for Word, etc.) and do a "Command open" from the appropriate program. When you then save the file, it will revert to the appropriate icon and file type.

However, I'm also running into instances where the program itself turns into a Unix file-- that has me stumped.
 
I'm not sure what you mean by "Unix executable file". I assume you mean a file not attached to any application which also has executable privs. If this is the case, you should be able to simply add a prefix to it (not necessary but perhaps useful) and do the control-click "Open With" trick [which can also be done by typing command-I ("Get Info") when the file is selected ] and setting the proper application.
 
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