A 144 KB PDF named 23c020, describing a component in the 23C series, which by usual convention are mask-programmed ROMs; 020 normally corresponds to 2 Mbit. The file name carries no maker or revision, so the document itself should be consulted for those details. It is useful for pin identification, timing and supply requirements when servicing older boards that store firmware in ROM, or when looking for a programmable equivalent. Check the part marking against this number before probing or replacing the chip.
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.