How to read file contents into a variable in a batch file?

This batch file releases a build from TEST to LIVE. I want to add a check constraint in this file that ensures there is an accomanying release document in a specific folder.

"C:\Program Files\Windows Resource Kits\Tools\robocopy.exe" "\\testserver\testapp$"        
"\\liveserver\liveapp$" *.* /E /XA:H /PURGE /XO /XD ".svn" /NDL /NC /NS /NP
del "\\liveserver\liveapp$\web.config"
ren "\\liveserver\liveapp$\web.live.config" web.config

So I have a couple of questions about how to achieve this…

1. There is a version.txt file in the \\testserver\testapp$ folder, and the only contents of this file is the build number (for example, 45 – for build 45)
   How do I read the contents of the version.txt file into a variable in the batch file?

2. How do I check if a file ,\\fileserver\myapp\releasedocs\ {build}.doc, exists using the variable from part 1 in place of {build}?