To associate a file with a .txt or .rtf extension with WordPerfect, go into the Windows Explorer and hold down the shift key and right click a file with one of those extensions. You will be given a list of choices. Choose Open With.... You will be given the Open With dialog box. Go to the bottom of the list and choose WordPerfect. Also, make sure that you check the box for the "Always use this program to open this type of file". Then click OK. WordPerfect should then open the file that you just associated with it. Repeat this procedure for every file that you want to associate with WordPerfect.
Now open the Windows Explorer and click on View and then Options. You should see the Options dialog box. Click on the File Types tab at the top of the box. You should see a list of associated file types. Find the Text Document file association and click on it. You should see the file type details telling you that this file type should be opened with WPWin. If it is not associated with it, click on the edit button and in the Actions box click on open and then click on the Edit button. In the Application used to perform action: box put in the path and executable name to the WPWin application. If you are not sure of the the exact path, click on the Browse button to help you find the WordPerfect file. Once you have filled the box in with the appropriate information, click OK and then Close. The file should now be associated with WordPerfect.
Hope this helps!