Can I clone an ESD.dmg file to an external disk without having admin password?

I have one Mac running 10.7.5 and another running 10.6.8 that can be upgraded to 10.7.5. Unfortunately, I don't have an admin password for either, because the previous owner of the first died suddenly and the owner of the second -- that's me! -- can't remember the password. I'm trying to create a bootable external volume from an ESD dmg file but when I follow the procedures for doing it using the Disk Utility Restore option, it demands a password even though I'm not trying to modify anything on the computer.

Is there any way of getting around this using, perhaps, dd?

If I borrow access to another Mac, does it matter what OS version it's running if I want to use Restore? (I couldn't run the installer on a Mac running 10.11. It said something about operating system incompatability.)

You can just set a new admin password and then you're able to enter the password for cloning the ESD.dmg file (which you'll then perhaps not even need at all).

You can set a new password by doing the following:

1) Power on the Mac while holding down the Cmd key and the S key

2) When the Mac has booted into single-user mode, type the following commands:

mount -uw /
launchctl load /System/Library/LaunchDaemons/com.apple.opendirectoryd.plist
passwd roger

You need to replace "roger" with the actual account name for your admin user.

When you're done, restart the system by typing this command:

reboot

Now you should be able to login with the newly entered password.

For others: If you're running a newer version of macOS (10.8+) you can do the same in a much simpler way by holding down the Command and R keys while booting up to start in Recovery mode. From there open Terminal from the Utilities menu. Enter the command resetpassword and you'll be guided through the rest of the process.