PDF document of 577 KB for the AD620, filed in the schematic category although a part-number name like this normally indicates a component datasheet. The AD620 is widely known as an instrumentation amplifier from Analog Devices, with gain set by a single external resistor. Technicians use such a document to confirm pinout, supply range and typical application circuits when checking sensor front ends or measurement boards. Any PDF reader opens it; compare the package marking on the board with the variants listed before substituting a 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 @cyberlanelectonik. 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.