No need to read the backup file manually.
RESTORE HEADERONLY FROM DISK = <path to backup file>
Among the columns are SoftwareVersionMajor, SoftwareVersionMinor and SoftwareVersionBuild that tell you the version and service pack of the server that the backup was taken from.
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability