Large 9.85 MB PDF datasheet named doc6120, a document number that does not state the component. The doc-number format corresponds to Atmel literature codes, and a file of this size usually means a full microcontroller datasheet with peripheral chapters, register maps and electrical specifications. Open it to read the device name on the cover page. It is helpful for identifying pins, debug and programming interfaces and supply rails, but verify that the chip marking matches the variant described before tracing signals or reprogramming the part.
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.