Portable Document Format (PDF) is a file format used to reliably present and exchange documents, independent of software, hardware or operating system. They are compatible with most systems, more secure than other files and save storage space. They contain links and buttons, form fields, audio, video, and business logic. PDFs can be signed electronically and easily viewed using free Acrobat Reader software. Businesses use PDF documents and they rely on reliable data entry companies to provide PDF conversion for their eBooks, invoices, and forms among other documents.