Symantec Corporation does not have Windows 8 support for PGP/Symantec Encryption Desktop products yet. This may come later this year. Please subscribe to:
http://www.symantec.com/docs/TECH199095
To stay informed on this.
Note: Touchscreen tablet support at the preboot screen won't be available for some time (on Windows 8 or not) with regard to Drive Encryption. This is due to a requirement of drivers to use this. So that is another limiting factor that I see currently to use the Surface Pro tablet with PGP.
Note: You could still use an USB keyboard or the surface pro docking station (with the keyboard) as a workaround.