Datasheet in a 2.90 MB PDF, named only doc6310 and therefore not stating which component it covers. The doc-number scheme was used by Atmel for its technical literature, and the cover page names the device. At this size it is likely a fairly complete datasheet with pinout, electrical characteristics and functional description. Use it to locate supply, clock and programming pins when diagnosing a board, and confirm the chip marking and package against the ordering information before trusting any pin mapping.
The button opens the matching file on RM Schematics, or a source page if it is not catalogued there yet. The original attachment is from @datasheet. Enginerys does not host this file.
How to open a .pdf file
The standard format for schematics, block diagrams, power-sequence charts and service manuals.