Assuming you didn't try to save the files after looking at them, they should be fine. Rsr's are binary files and you really shouldn't mess with them in a text editor. To change the file associations, open any folder and goto the view menu -> folder options and look at the file types tab. From there you can change the associated program for each file type from wordpad back to Poser. I don't think having them under wordpad will affect their functionality in Poser, just the display in Windows Explorer.

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