Boardview file in BRD format for a board coded UM3B-MB-E. The name gives no brand or model, and the MB-E ending likely marks the board revision. Boardview files show component placement, part references and net connections on both sides of the PCB, which helps find test points and follow a shorted rail. BRD files open in viewers such as OpenBoardView, FlexBV or Boardviewer. Check that the code on the PCB matches before relying on part locations.
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 @ITHINKHS. Enginerys does not host this file.
How to open a .brd file
The most common boardview extension. Several unrelated formats share it, which is why one viewer opens a .brd and another refuses it.