How can i include a pre-built binary file into buildroot generated image?
I have tried to include the binary file into appropriate folder in build_dir but every time i try to do make the image is being created without the file.
You can use a root filesystem overlay.
See chapter Project-specific customization in the Buildroot manual.
Just in case someone is looking for a easy fix you can add the files to buildroot-dir/files folder. The file should match the exact directory structure. For example you want to put the file in /usr/bin in the image then keep the file in buildroot-dir/files/usr/bin and rebuild the image.