v3 Ramdld 827 is so you can successfully flash or backup v3 with 8.29 bootloader
BL 828 to 7do is the downgrader flash to assist in downgrading the bootloader
Pack de Bootloader is self explanatory. its a folder containing different bootloader for v3
R374 BL 7.do is the 7.do bootloader flash
if you wish to downgrade your v3 from bootloader 8.29 to 7.do there is a simpler way than described in this guide. the purpose for downgrading is for modding purposes only. you can unlock the phone, flash custom MP's, etc.