Portable Document Format
Data format developed by Adobe Systems Inc. and used for exchanging and processing electronically stored, formatted documents with text and images, independent of hardware or software.
This makes it possible to send a formatted document to a computer screen or printer and have it look exactly the way in which it was created.
One of the special features of the format is that texts and graphics are stored in vector form, meaning that the resolution of their representation is dependently solely on the output device (monitor, printer).
You need Acrobat Reader to read PDF files.