PDF datasheet of 634 KB carrying only the reference doc6258, which does not reveal the device it covers. The doc-number naming corresponds to the literature codes used by Atmel for microcontroller, memory and peripheral documents, and the part name is shown on the cover page. After identification, it is useful for checking pinout, operating voltage, register descriptions and package dimensions. Confirm that the device marking and document revision match the chip on the board you are working on before trusting pin or timing data.
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.