Component name sheet for the Samsung SM-A21s, a 3.81 MB PDF from the schematic set. Judging by the title, it identifies board parts by designator so a component named in a circuit page can be located on the real PCB. Technicians keep it open alongside the section schematics while hunting a specific capacitor, coil or IC during fault finding. Any PDF reader opens it; zoom in for fine labels. Make sure the phone is an SM-A21s, since layouts differ across Galaxy A models.
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 @phoneSchematics. 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.