This is the info I receive regarding ACER.
How to disable secure boot and access the boot menu on the Acer
To boot from external media that has an unsigned bootloader, a supervisor password must be set in the BIOS to change the Secure Boot settings. Also, the F12 boot menu is disabled by default. Here is how to change those settings on an Acer Aspire ES1.
In order to get to the BIOS setup, repeatedly hit the F2 key as soon as you power on the machine.
Hit the right arrow key to get to the Security tab and hit Enter to set a Supervisor Password.
Then hit the right arrow again to get to the Boot tab and hit the down arrow and Enter and the down arrow again to set Secure Boot to Disabled.
Now we can clear the supervisor password. Go back to the Security tab by hitting the left arrow and hit Enter to set the Supervisor Password again. Type your password and hit enter. Then hit enter again twice to clear the password.
To enable the F12 boot menu, hit the left arrow to get to the Main tab and hit the down arrow 3 times to get to F12 Boot Menu, hit Enter, and press the down arrow and Enter to enable it.
Finally, hit the F10 key followed by Enter to save the settings and reboot.
Now you can boot off of external media like a USB drive by hitting the F12 key repeatedly immediately after power on.