As already posted you can use Cross Reference from the Tools menu, this runs a utility that has historically been referred to as SCOUT and does cross-referencing and sheet numbering. If you are new to this tool then there are a number of resources including the on-line help and further resources on SupportNet to help you with setting up the tool to get the output you require.
Was-Is Comparison of EXP2005.x Scout utility and EE2007.1 cross Reference utility
Every time Scout is run it overrides the placement of the XREF attribute
Cross Reference Not Added to Dangling Nets (iCDB)
Scout is Ignoring Second and Subsequent Bus Elements of a Bundle When Generating XREF
xrefs are not appearing in my design
How to record but not place XREF information using Scout?
Also forgot to mention that in EE7.9 and PADS 9.2 you can use 'links' to dynamically link nets between sheets, but currently this only supports flat designs. In EE7.9.1 (PADS9.3) these are further enhanced to support full cross-referencing and will eventually replace SCOUT as a utility. See http://supportnet.mentor.com/reference/tutorials/index.cfm?id=10591 for details.
I suggest continuing using scout.ini for now until dynamic link extensively tested.