The preferred way for adding RMStore to your project is using CocoaPods:

pod 'RMStore', '~> 0.7'

This will add the RMStore core to your project. RMStore also provides reference implementations for receipt verification and transaction persistence, each with its own subspec that can be added independently:

pod 'RMStore/AppReceiptVerificator'
pod 'RMStore/TransactionReceiptVerificator'
pod 'RMStore/KeychainPersistence'
pod 'RMStore/NSUserDefaultsPersistence'

Bear in mind that AppReceiptVerificator depends on the OpenSSL pod. It might take a while for it to build the first time.

If you don't want or can't use CocoaPods, you can simply copy the files you need from the RMStore directory. The RMStore core is a single class.