Steps to Flash .Pac Stock Rom on Android Smartphone :

                              Step 1: Enable USB Debugging on your Android Smartphone. To enable USB debugging, Open Settings > Developers Option > USB Debugging > Tick to Enable.
(Developers Option is hidden for Android 4.2.2 or above, to unhide Go to Settings > About Phone > Built Number (Tap on it for 5-8 times) ( if u dont know click here )

                              Step 2: Download Stock Rom (.pac) for your Android Device.

                              Step 3: Download and extract Spreadtrum Upgrade Tool on your computer. After extracting, you will be able to see the following files:

                              Step 4: Now, open UpgradeDownload.exe

                              Step 5: Once Spreadtrum Upgrade Tool is launched, connect your Android device to the computer (make sure your device is switch off).

                              Step 6: Once your Smartphone is connected successfully to the computer, click on the Load Packed Button and add the .pac file (stock rom which comes as .pac).

                             Step 7: Once you have successfully added the .Pac file in Spreadtrum Upgrade Tool, click on the Start Downloading button to begin the flashing.

                            Step 8: During the flashing process your device will restart automatically. Once flashing is completed, you will be able to see the Green Passed Message in Spreadtrum Upgrade Tool

                            Step 9: Now you have successfully flashed your Android Device using Spreadtrum Upgrade Tool. Once your Android Device is successfully restarted, Go to Settings > About Phone > Check firmware.