How we can apply the permission on Document library on the basis of the location??????? such as User ABC can access the Doc Library from India but not from US, same user with same login.
Claim providers came to mind. You could write a custom provider that aguments the user claim with a value that identifies the location they are logging from. Then, build the permission in the library based on the claim.
The most difficult part would be implementing the claim provider infrastructure (at last - it can be if it's the first time you implement it) and finding a reliable way to detect the user location when they log-in.