PDF files (the name stands for Portable Document Format) are known for comprising texts, images and 2D graphics in a manner that can be easily shared across the Internet.
PDF files have become popular due to the fact that the documents' creator can assign passwords that would protect the contents against unauthorized usage or printing.
Desktop applications that deal with editing PDF files will allow users to modify and extract text from any PDF.
Some PDF editors will also offer users the possibility to add new fields, fill forms or change passwords.