VectorWorks has this built-in to the program. However, I'm not sure if it's as good as a dedicated converter. It also depends how the PDF file originated. If it was created from the CAD application, it should have the vector data embedded in it, to allow conversion fairly easily and accurately. However if it was scanned, or created as a bitmap image, it's a bit harder. You'll need to use a bitmap tracing application. The free, open source multi-platform application Inkscape has a really good bitmap tracing algorithm, but there are other professional tools that can do it for you. This is harder and less accurate, and the resulting files won't necessarily be 'clean' CAD files. By this I mean that the lines may be made up of lots of little line segments, resulting in a large file that is much harder to use.
The same goes for the X and Y PDFs, which are basically equivalent if you have a PDF/X and a PDF/Y. If you don't, and your PDF is of a type that wasn't available before, it won't change, and will remain a PDF. And for those of you worried about the security of your document, don't worry. The PDF is signed, with a password. The only other way to see it is if you have physical access to the document, and you know its passphrase. But for those people who like a PDF/A that just works, and never breaks, and doesn't require extra features, I've got a handy PDF cheat sheet. If you have any questions or comments, or would like to report a bug, please email me, and I'll get to it as quickly as I can. Happy document making! —Steve PSA: Don't forget your own password to ensure the security of your PDF/A.