Hello
If it is a valid RTF file, you should be able to open it in any application, including AppleWorks 6, which supports RTF file.
How are you opening the file in question? Double-clicking? Then try drag-dropping the file onto AppleWorks icon (in Dock, e.g.) As far as I can tell, AppleWorks 6 can open (actually import) RTF file, especially if the file has been exported from AppleWorks 6 itself.
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If, by any chance, AW6 rejects it, try drag-dropping the file onto TextEdit.
Just make sure the following 2 things :
1) The file in question has the name extension as ".rtf"
2) In TextEdit > Preferences…, some option named "ignore rich text commands in RTF files" or the like is NOT CHECKED.
Good luck,
H