A 253 KB PDF for the JEDEC-registered 2N5879, tagged RE without explanation and indexed as a schematic, though it is probably the part's datasheet. The 2N prefix denotes a two-junction semiconductor, typically a transistor. Inside you can expect pin assignment, package dimensions, maximum ratings and performance curves. Repair technicians use it to confirm terminal order before desoldering, interpret meter readings and compare candidate replacements against the original's specifications.
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.