PayPal .NET SDK is our official Open Source .NET SDK for supporting PayPal Rest APIs. Checkout all the supporting documents, samples, codebase from the following links
Find everything from Installing, running Samples, Configurations in .NET SDK Wiki
Check out the sample code for using SDKs to call all PayPal APIs.
Explore a Pizza Store developed using PayPal .NET SDK
Checkout the Official PayPal REST API Reference, explaining all API Models
Download the latest .NET SDK Release