[XDA Assist] nimphus:
I did what this guide told me to do:

Rooting Information: As we said already, once your device is rooted, warranty will get void. However, you can reclaim the warranty by applying official firmware update and then resetting the flash counter to 0 using apps like TriangleAway. To confirm if you successfully rooted your Android device or not install an app called “Root Checker” which is available for free from Google PLAY store.

Warning!

We at True Android produce tutorial to help out fellow Android users but all this guide are educational purpose only. You should try this guide at your own risk. Neither we nor the developer should be responsible if your Android device experience a damage after following this tutorial. Also remember,this guide is only applicable for Galaxy Tab 3 10.1 GT-P5210. Don’t try this guide in any other Android device. It may hard brick your device.

Pre Requisites:

As there is always some risk involve while you install anything other than what you have presently. It’s always recommended to follow our pre-requisites to stay safe.

1. Backup your device data. You can follow our ultimate backup guide.

2. Make sure your device have at least 60% battery power. You can install an app like Battery Notifier BT Free on your Android device to check it easily.

3. You already have USB Driver Installed for Galaxy Tab 3 10.1 GT-P5210 in your PC. [Download USB Drivers]

4. Make sure USB Debugging is enabled otherwise you won’t able to transfer file between PC and mobile. [Guide].

So, you done everything that we mentioned above, right! Now, you are ready to move towards next stage of this guide where we summed up detail instruction on how to root Galaxy Tab 3 10.1 GT-P5210 running latest official Android firmware.

Remember, it’s very important for you to follow everything that we mentioned below to successfully root your Galaxy Tab 3 10.1 GT-P5210 on official Android firmware.

Complete Rooting Tutorial Of Galaxy Tab 3 10.1 GT-P5210

Step 1: Download CF-Auto-Root-santos10wifi-santos10wifixx-gtp5210.zip and Odin v3.09.

Step 2: Now extract CF-Auto-Root zip file at a convenient location in your desktop; you should get a .tar.md5 file within extracted folder.

Step 3: Extract Odin zip file and you will get Odin3 v3.07.exe along with few other files.

Step 4: Now turn off your Galaxy Tab 3 10.1 GT-P5210 and wait 5-6 seconds for vibration to confirm complete switch off. Then boot it into the Download Mode, to do that press and keep holding the Volume down and Power Button together. When a warning message is displayed press on the Volume Up button to entering the Download Mode Menu.

Step 5: Now run Odin3 v3.07.exe that you get in Step 3 as an Administrator because Admin privileges is required to complete this installation process smoothly.

Step 6: Now it’s time to connect your Galaxy Tab 3 10.1 GT-P5210 with your PC using USB cable. Do it and you will see a message under Odin’s message box in the bottom left saying “Added!!”. If you don’t get it then you should try another USB port (try USB port located in back of your desktop PC cabinet). If this still can’t solve your issue then you should reinstall USB driver for your device. However. if you successfully see the “Added!!” message in Odin then you are ready to go in next step. You should also see COM port with a number in Yellow if you successfully added your device.

Step 7: Select following file in Odin at respective button:

Click the AP Button, and select that CF-Auto-Root-santos10wifi-santos10wifixx-gtp5210.tar.md5 file that you get in Step 2. Old Odin user click on PDA button instead.

Step 8: In Odin window, make sure Auto Reboot and F. Reset Time checkboxes are only two that are selected.

Step 9: To make flashing safe for you double check everything that we mentioned in Step 7 and Step 8 above. Now, once you are ready, hit the START button to begin the flashing process.

Step 10: Once installation is done, your device will reboot automatically and soon you will see a PASS message with green background in the left-most box at the very top of the Odin. You can then safely unplug the USB cable to disconnect your device from computer.

That’s it! Your Galaxy Tab 3 10.1 GT-P5210 running on official Android firmware is now rooted. You can now install apps that require root permission as well as access system files. To confirm if you successfully rooted your Android device or not install an app called “Root Checker” which is available for free from Google PLAY store. You can now visit this Best Apps For Rooted Android Devices (Android Phones & Tablets). If you face any root issue then do this: Connect your device to internet then update SueperSU app binary. After that, open SueperSU again and turn off KNOX notification from there.

But I accidentally disconnected my Tab from my PC before getting the "Passed" on the Odin.exe.

How do I unbrick this phone?