Disabling driver signature enforcement in Windows 8/8.1 is easy enough using the advanced startup options.
But it is also possible by command line. This method is not as well known, but has certain advantages - it works on Windows tablets which have no means of selecting the options during startup and I did not need to reboot.
I encountered a problem when trying to install an unsigned driver on an Asus Vivotab Note 8 tablet running Windows 8.1 32-bit using the advanced startup options method. After restarting and reaching the options screen, I had no way of selecting an option - the tablet has no keyboard, there was no access to the onscreen keyboard and the touchscreen didn't work. Plugging in a USB keyboard did not solve the problem, it would not work during startup (even after disabling secure boot).
Caution: Never install an unsigned driver unless you are absolutely certain you know what it is for, why it needs to be installed and that it came from a trusted source. These security features are there for a reason, not just to inconvenience us. If you are not familiar with using the command prompt then do not proceed further
1) Disable secure boot in the UEFI.
2) Open an elevated command prompt (even if you are using an administrator account). The easiest method is right-click on the start menu icon and select 'Command Prompt (Administrator)'.
BCDEDIT -Set LoadOptions DISABLE_INTEGRITY_CHECKS
BCDEDIT - Set TESTSIGNING ON
I did not need to reboot, but some sources say it is necessary at this stage.
If you receive an error message check that secure boot is disabled and that you are using an elevated command prompt.
4) Install the unsigned driver.
5) To re-enable driver signing enforcement enter:
BCDEDIT -Set LoadOptions ENABLE_INTEGRITY_CHECKS
BCDEDIT -Set TESTSIGNING OFF.
6) Remember to enable secure boot again when you have finished.
If you need to do this regularly it should be possible to run two batch files and save a bit of typing.