For lots of files, there are paid tools just for converting from old formats to new ones, like File Merlin or WordPort.
For a budget of zero dollars, Word used to have a package of import converters that would handle files created by DOS versions of WordPerfect, WordStar, Amipro, and Word for DOS. These converters never came on the CD - you had to know they existed and then google them. And Microsoft discontinued them back in 2003. But they still work perfectly with Word 2003 (instructions for using them with later versions are available)
The DOS import converters were distributed as wdsupcnv.exe. They are no longer available on Microsoft’s FTP site, but with a bit of patience you can find a live download location with Google if the following link goes dead.
