Short summary version of the tiny28 datasheet, indicated by the s suffix and the small 139 KB size, matching the Atmel AVR ATtiny28 microcontroller. Summary editions usually keep the feature list, pin configurations, register summary and ordering information while leaving out the detailed peripheral chapters. That makes it handy for a quick pinout check on the bench. For electrical limits, timing or programming specifics, the full datasheet is the better reference, and the part marking on the board should match before relying on either.
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.