Use software like WinRAR (Windows), 7-Zip (Windows), or The Unarchiver (macOS).

Right-click only the first file ( SDF part 1.rar or SDF.part1.rar ) and choose "Extract Here." The software will automatically pull data from all parts to reconstruct the original file. If you can tell me: Where you found or downloaded this file?

This is a part of a multi-volume RAR archive, which is a common format for compressing files.

"SDF" could refer to many things, often Spatial Data File formats (GIS data) or, in the context of file sharing, it is frequently used to split large game assets or datasets into smaller, manageable chunks. How to Use "SDF part 3.rar"