The PDFfiller API allows its users to build applications that interact with PDFfiller over the HTTP REST methods. All API communications are SSL encrypted and must be made over HTTPS protocol. We recommend using an SSL version higher than 3 and a TLS version higher than 1.0. For authentication, we support OAuth2 authentication with password and authorization_flow grants. JSON is returned for all API responses except file downloads. PDFfiller provides API client libraries for specific languages to help convert API objects to the language format.