Datasheet for an Atmel AT91SAM ARM-based microcontroller, 3.90 MB PDF. The name gives only the family prefix, so the exact device, such as SAM7 or SAM9, must be identified from the document's cover page. Such datasheets cover pin multiplexing, peripherals, memory map, electrical characteristics and package drawings. Technicians use them to locate supply, reset, clock and JTAG or debug pins when diagnosing a dead board. Check that the marking on the chip matches the part covered.
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.