A 43.6 KB PDF for the 3N247, filed among schematics but named after a discrete component, so it is most likely a datasheet. The 3N prefix belongs to the JEDEC registration scheme used for devices with four leads, such as some FETs and optocoupler-type parts. A technician would use it to read the pinout, package outline and electrical limits before replacing or testing the device. Open it in any PDF viewer and confirm the part marking on the board matches, since neighbouring 3N numbers can differ in ratings.
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.