You have created an image of an SD card containing a Linux operating system. Afterwards you want to access and extract files of the image, but do not have a spare physical storage available or you are working on a virtual machine.
Unfortunately, it is not an ISO image which could be mounted by Windows itself or opened with 7-Zip.
Run Win32DiskImager to create your image.
Install ImDisk. It lets you mount Linux SD card images and similar drives under Windows.
Install Ext2Fsd. With this tool, you can access EXT2, EXT3, EXT4 and VFAT partitions under Windows.
Now mount your Linux partition with Imdisk and you should be able to access the files and folders via Windows Explorer.