Datasheet in PDF format, 1.39 MB, labelled doc6213, which is a document code and does not name the part. Atmel used this doc-number pattern for its technical literature, and the specific device and revision are printed on the first page. A document of this size typically includes pinout, electrical characteristics, peripheral descriptions and package drawings. Treat it as a reference once the part is identified, and compare the marking on the board's chip with the ordering information section before using any pin or voltage value.
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.