PDF document named after the BQ25601, a Texas Instruments single-cell lithium-ion battery charger IC used in phones and other portable devices. Although it is filed as a schematic, a file of this name and size is most likely the manufacturer datasheet. That would include pinout, typical application circuit, register map and electrical limits. Repairers check it when a device will not charge, to verify input, system and battery pin voltages and the values of the external parts. No device or board is named, so match it to the IC actually fitted.
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 @uzb4422. 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.