PDF document for the CS8573E from Chipstar Micro-electronics, catalogued as a schematic but most likely the component datasheet or reference design. It should give the pinout, block diagram, electrical ratings and an application circuit. Datasheets like this help a technician find the supply, input and output pins to measure, check expected voltages and spot a failed part or substitute. The name does not mention the device it was used in, so the document is best read as a generic reference for 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 @pdf_servicemanual. 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.