how to restore single .backup file (backup of multiple database in a single backup ) on windows having postgreSQL installed

Hop did you create the .backup file? Which exact(!) command did you use?

Backup file is automatically created by the script written on production server and then this backup is updated on the standby server through the script.

there is no direct command to take the backup but i am sending you the link
which can probably help u.
[URL="http://www.thegeekstuff.com/2009/01/how-to-backup-and-restore-postgres-database-using-pg_dump-and-psql/"]

Again, WHAT was the specific syntax that YOU used ??? the pg_dumpall?

Rather than create a single huge backup file with the entire server's contents dumped there, it's often more 'friendly' to create individual database backups.
If it's a single file, copy the backup file to a working file, then delete everything in front of the first portion of text referencing the database name in question, and everything after the last line of SQL that references your target database.

Then, execute the backup SQL work file, using pgadmin or pSQL.