Usually, in order to install a custom recovery like TWRP on your Sony Xperia Z3, your device must be bootloader unlocked, but unlocking bootloader will lose your phone’s warranty and delete the DRM security key from the Xperia Z3. DRM key is required for the advanced camera functionality on Z3.
In this tutorial, we will show you how to install TWRP custom recovery on your Xperia Z3 without locked bootloader. However, this tutorial required a rooted Xperia Z3 (read here to know how to root Xperia Z3 with locked bootloader). Custom recovery provides a number of advanced features over and above the stock recovery, such as Nandroid (system dump) backup.
How to install TWRP Recovery on Xperia Z3 with locked bootloader
1. Install a root file explorer like ES File Explorer on your phone and mount /system rw.
3. Connect your Z3 to your PC via USB cable and double click install.bat (from your extracted folder).
4. Choose option 1 and follow the on screen instructions. The phone will test reboot to TWRP recovery.
5. Reboot your phone and you are good to go.
Congratulations, you have been successful to install TWRP on Xperia Z3. You will see a new application NDR Utils installed on your Xperia Z3, which helps you boot your phone to the chosen recovery (source – XDA)