Firstly, it’s common knowledge that you can right click a word with a spelling error and click ‘Add to Dictionary’.
This is useful if you are using abbreviations or fictional words.
You can also turn off spelling and grammar check completely to remove those pesky red and green lines.
To disable spelling and grammar check in Word for only one document, click File, then Options, then click Proofing.
You must then tick the two options for hiding spelling and grammar mistakes in the document you are currently writing in.