There are actually several auto format options that can cause the problem. You need to turn all of them off to correct the problem.

You might check the suggestions from the following link:

I've turned off automatic formatting options, and Word still formats my document.

First, make sure that you've turned off the options on the correct tab. When you click AutoCorrect Options on the Tools menu, you can turn off two types of automatic formatting:

The AutoFormat As You Type tab contains the automatic changes Microsoft Word makes as you type.
The AutoFormat tab contains the automatic changes Word makes when you format the document in a separate pass.
If neither of the above addresses your problem, try one of the following:

Unwanted symbols keep reappearing

If you've cleared the Hyphens ( -- ) with dash ( — ) check box on the AutoFormat As You Type tab, and Word continues to insert symbols, one or more symbols may be set up as AutoCorrect entries.

On the Tools menu, click AutoCorrect Options, click the AutoCorrect tab, and then see if the Replace box contains the symbol Word is automatically replacing. You can either delete the entry by selecting it from the list, and then clicking Delete, or turn off AutoCorrect completely by clearing the Replace text as you type check box.

Text style changes unexpectedly

If Word keeps applying unwanted styles to text, you can have Word prompt you before updating styles. On the Tools menu, click Options, click the Edit tab, and then select the Prompt to update style check box.

Word keeps formatting text as headings

If Word continues to format text as headings even after you've cleared the Built-in Heading styles check box on the AutoFormat As You Type tab (Tools menu, AutoCorrect Options command), clear the Define styles based on your formatting check box under Automatically as you type.

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