Part number 1SV251 is all the file name provides for this 63.3 KB PDF, which is catalogued as a schematic. The JIS-style 1S prefix denotes a diode, and the 1SV designation is Toshiba's code for varactors. The content is therefore most likely a one-device data sheet with ratings, curves and a package drawing. When this marking turns up on an RF board, the sheet helps you verify orientation and read the tuning characteristics. You can then choose a compatible replacement with confidence. It opens in any PDF software.
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 @cyberlanelectonik. 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.