I recently had to reinstall Windows on another computer. When I went to transfer some files over from my external hard drive, the drive wasn't recognised due to it being partitioned in ext4.
After a bit of searching I found some freeware software called ext2explore. ext2explore doesn't need to be installed, it is a standalone application, just download, extract the folder and click .exe to run the software.
The software was able to locate my hard drive allowing me to browse the files on the drive and save any folders or files to the Windows desktop.
ext2explore can be downloaded by visiting https://sourceforge.net/projects/ext2read/files/Ext2Read%20ver%202.0/ext2explore%202.0%20beta/