In Windows 8 and later editions, there is a built-in spell checker that is embedded in your system. The spell checker and auto-correct is supposed to work over different sections of Windows uniformly. In many scenarios, you might find the auto-correct feature productive, but if you think it is not working to your expectations, you may want to turn off this feature. You can manually turn off the auto-correct feature in following way:
Manually disable Spell Checker & Auto-Correct
In order to deactivate the auto-correct feature, press
Windows Key + C. Click
Settings, this will take you to PC Settings. In the left pane, navigate to
PC and devices ->
Typing. In the right pane of this screen, turn Off or move the slider to left for options
Autocorrect misspelled words and
Highlight misspelled words. This should disable the auto-correct feature instantly.

You can also try something different to get rid of auto-correct feature. In this scheme, you need to add your regional language to Windows 8.1. Just navigate to
PC Settings ->
Time and language ->
Region and language, in the right pane, click
Add a language.

So far, I’ve added Hindi as the secondary language. Now, when you’re writing something, if the auto-correct feature is not working according to you, press
Windows Key + C to switch to secondary language. As after switching, you’d have less misspelled words. In this way, you can switch between languages instantly, just by pressing two keys combination.

However, still if you want to disable spell checker and auto-correct feature completely, try these steps:
Completely Disable Spell Checker & Auto-Correct In Windows 8.1
1. Press
Windows Key + R and type following and hit
Enter:
C:\Windows\System32
2. In the System32 folder so opened, type
MsSpell in the search box and hit Enter. This will result up four files as shown below. Checkout
this thread to add Take Ownership to right click context menu to take ownership of these files. After adding the Take Ownership effect, right click over these four files individually and take their ownership.

3. After taking ownership, rename these files to something that you can remember. For example, rename
MsSpellCheckingHost to
MsSpellCheckingHost_old. After renaming the four files, reboot the machine, you have now successfully disabled the spell check and auto-correct feature.
In the future, if you again want to restore or re-enable the auto-correct feature, just rename these files to their original name and turn on both the options
PC Settings ->
PC and devices ->
Typing ->
Spelling.
twc