The name of this 115 KB PDF gives the part number 1SS355, a small-signal silicon diode by the JIS 1SS convention, and carries no device or board details. Although it sits in the schematic category, the content is most likely a component data sheet with pinout, marking, ratings and outline. Use it when a switching or clamping diode on a board fails and an exact or equivalent replacement is needed. Any PDF viewer opens it; check the original marking and package 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.