Click to place the cursor in any area within the document where you want to insert a checkbox.
Click the "Custom Quick Access Toolbar" button in the upper left corner of the document window. Click "More Commands," "Popular," and then check the "Show Developer Tab in the Ribbon" box.
Click the “Developer” tab now visible in the Ribbon, and then click the “Legacy Tools” option from the Controls group.
Click the “Check Box Form Field” option below the Legacy Forms section. The checkbox will be added to your document. To remove gray shading from the checkbox, click "Legacy Tools" again, then click "Form Field Shading" resembling a button with the letter "a" on it, to remove the shading.
Click "Design Mode" located in the Controls group within the Developer tab to ensure that design mode is turned off.
Click the "Developer" tab and then click the "Protect Document" option from the Protect group. Click the "Restrict Formatting and Editing" option.
Select the box next to the "Allow Only This Type of Editing in the Document" field below the "Editing Restrictions" field and then select the "Filling in Forms" option.
Click the "Yes, Start Enforcing Protection" option below the Start Enforcement heading and then enter a password into the "Enter New Password (optional)" field to protect the document and confirm the password. If you don't select a password, anyone who works in the document can alter your editing restrictions. Click "OK" and you will now be able to click on the checkbox that you inserted.