The largest item in this group at 335 KB, this PDF is named 2SC5339 and gives no device or board information. Under JIS numbering, 2SC designates an NPN bipolar transistor for high-frequency applications, so the document is most likely its datasheet, perhaps with more characteristic curves or package details. Use it to confirm pin order, ratings and gain grades when testing or replacing the part. Any PDF viewer opens it; verify the marking and package of the real component first.
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.