A: Yes, but you must first update Snow Leopard to Mac OS X 10.6.8 (build 10K549) and install the Mac App Store update. Sierra requires at least Lion (10.7.5) from the App Store, but the DMG method bypasses that by creating a bootable USB.
A: The file might be locked or corrupted. In Terminal, try: Download Mac Os Sierra Dmg
Simply keeping a DMG on your hard drive does not help if your Mac won’t boot. You need a bootable USB drive (8 GB minimum, 16 GB recommended). A: Yes, but you must first update Snow
Note: This command works on macOS Sierra and newer systems. If you are running an older Mac or a different OS, use the next method. use the next method.