Normally we'd admonish you to give more information. "It doesn't work" doesn't tell us anything.
But I am totally puzzled by your use of a regex validator on a dropdown selection list. When the choices you can make are limited by what's in the list, using regexes to validate them doesn't make any sense. :confused:
An IDE is no substitute for an Intelligent Developer.
I’ve looked at a lot of different solutions, and in my humble opinion Aspose is the way to go. Here’s the link: http://aspose.com