"The file appears to be corrupted"

[TKerr]

I am using Word 2003. With service pack 2, I was able to open old WordPerfect
5.x files. However, after the installation of service pack 3, a window pops
up stating, "The file appears to be corrupted" and I cannot open the file.

I could not find anywhere at the Microsoft site, what Service Pack 3 changed
that causes Word 2003 to believe a WordPerfect 5.x file is corrupt.

I have tried saving the file from WordPerfect into RTF, but this removes the
auto paragraph numbering schemes my visual basic macro uses to automatically
assign paragraph styles, as well as generating a lot of ugly, unusable
characters.

I have tried saving the file from WordPerfect as Word 2.0, but that causes a
window to open that says, "You are attempting to open a file that was created
in an earlier version of Microsoft Office. This file type is blocked from
opening in this version by your registry policy setting."

I have followed the official Microsoft site instruction for editing the
registry, but Word still refuses to open a file saved in Word 2.0 format.

Any hints, clues or ideas?