In this tutorial, i'll show you how to extract FTF firmware and system.sin file using 7-ZIP and Flashtool. This method will work for any Sony Xperia phones that uses FTF. These programs can be downloaded from the internet
Note: Flashtool require Java JDK
Let's get started,
I have a FTF firmware file of Xperia Z3 Compact. I would like to see what's inside the firmware so I'm going to open the FTF with 7-Zip.
Right click -> 7-Zip -> Open archive
You will see the files inside FTF file. These .sin are images to extract .sin to partitions, example: System.sin copies to /system.
System.sin is the Android OS image, so extract that file
Wait, you can't open .sin file with 7-Zip. You'll need to Extract data first
In Flashtool: Click Tools -> Sin Editor. Select the system.sin file and click Extract data. It will some times to extract system.ext4 file
Open system.ext4 with 7-Zip
You can extract everything, customize the firmware/ROM and make it into a flashable.zip
I'll recommended to use PRFcreator to create stock firmware with your custom ZIP.