Pantone's cmyk values (or any of the value types) from the web site—or any web site's values for spot colors—are what I call "dumb" values. That is, they exist without meaning or context. This applies to the swatch books to some extent with te exception the swatch books are printed using the output profile that they specify in the books. But the cmyk values listed are only good for that particular profile.

Pantone's cmyk values vary depending upon the pdf's output profile. That is, they change depending upon the pdf output profile as they ought to. The only means to be reasonably accurate is to take the output condition into account.

The old, clunky and funky software they sell (it's terrible software, and that according to their tech support) can and does give accurate color model values. I have it and have used it for years even though it is a right pita.

Xara products will do the conversion properly if a output profile is used. Which means that you need to know what the print establishment is going to use by way of output profile.

Talk with the print establishment about leaving spot colors in the pdf. It is possible for some "real" print establishments to do the conversion at print time, which means exporting to a pdf profile that retains spot colors as spot colors. Most of the print establishments I use prefer to do the conversion as they have tweaked the Pantone look up tables to suit their presses. Online printers don't want spot color as spot color.

Xara applications are not color managed. You cannot trust what they show you on-screen. The only pdf viewing applications that are color managed are Adobe Reader, Acrobat and pdfToolbox.

Mike