Boardview in BDV format for a board labelled NM3-SI-MB-B. The name gives no brand, model or board maker, so identification depends on matching the PCB silkscreen. BDV files open in boardview viewers such as FlexBV and similar tools, and show component placement, pins and net connections on both sides. Technicians use them to locate parts, follow signals, find test points and check which components share a shorted net. At 408 KB it is a modest layout, so confirm the board number on the hardware before working from it.
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 @pepeelectronica. Enginerys does not host this file.
How to open a .bdv file
Text-based boardview produced by Honhan / Hon Hai test tooling, with lightly obfuscated content.