Dell archive referring only to a 5521 model, most likely the Inspiron 15R 5521, compressed into a 3.10 MB RAR. The name does not say whether it holds BIOS, EC firmware, a schematic or boardview, so extract it and check the contents before use. If it contains a firmware image, back up the existing SPI chip with a programmer before writing, and confirm the image size matches the chip capacity. For documents, compare the board number on the PCB with the files inside.
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 @laptop_bios_schematic. Enginerys does not host this file.
How to open a .rar file
Compressed archive — the usual wrapper for a schematic + boardview pair or a BIOS + EC set.