Based on your description, Word is behaving as designed. In a protected document with legacy check boxes, you can't type in any text. You will have to (temporarily) unprotect the document and add text form fields for users to add text.

What you can do is insert a section break and leave one section unprotected. It can then be edited (but there is a number of editing restrictions enforced on any protected document, even on unprotected sections).

Alternatively, if the document doesn't have to be backward compatible (to Word 2003 or earlier versions), you can make use of content controls instead. These will let you type freely outside of the controls.

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Stefan Blom
Microsoft Word MVP

Microsoft 365 apps for business
Windows 11 Professional