Short PDF repair guide for the Samsung B310E feature phone, focused on display faults according to its name. At 214 KB it is probably a single sheet or a few pages, likely showing the LCD connector area with marked tracks, jumpers or components involved in a no-display or white-screen problem. Technicians use such solution diagrams to check continuity between the connector and the processor and to bridge broken lines. Any PDF viewer opens it, and the board revision should be compared with the drawing first.
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 @Schematic_mobile_iran. 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.