Datasheet for the tiny22, a name pointing to the Atmel AVR ATtiny22 microcontroller, provided as a 933-935 KB class PDF of 935 KB. The name states nothing beyond the part, so revision and package coverage must be read from the document itself. Typical contents are pin descriptions, memory organisation, electrical characteristics and programming specifications. It is useful for verifying pin functions while probing a board, checking voltage and current ratings, and confirming programming details before attempting to read or rewrite the chip.
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.