An 804 KB full datasheet for the tiny15, consistent with the Atmel AVR ATtiny15 8-bit microcontroller. No revision appears in the name. The document is expected to cover pinout, internal oscillator calibration, ADC and timers, DC characteristics and the programming specification. Opened in any PDF reader, it lets a technician identify supply, reset and I/O pins on a populated board, verify measured voltages against ratings and prepare correct connections before attempting to read or reprogram the controller.
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.