Foxit PDF SDK is a software development kit designed to help developers integrate PDF functionalities into their applications. It provides tools for creating, editing, and viewing PDF documents, making it easier to manage PDF files within various platforms, including mobile and web applications. The SDK supports multiple programming languages, such as C++, Java, and C#, allowing developers to choose the best fit for their projects. With features like form filling, annotation, and digital signatures, Foxit PDF SDK enhances user experience by enabling seamless interaction with PDF documents.