Hi @KOLEVA Sonya (REGIO),
Thank you for posting your question in the Microsoft Q&A forum.
According to your concern, I've tested in my Word (version 19426.20076) and Word does not allow me to edit Header when Restricting Editing. It is likely that when enforcing protection (I'm testing with Filling in forms since I'm using checkboxes), headers and footers are treated as part of the protected section and Word does not allow editing headers/footers under form protection mode.

There are two workarounds for your situation that I suggest you can try:
1- Use a separate section for Names
- Instead of using header, you can add a section before your form for users to put their name there
- In the Layout tab > Break > in the Break Section, choose Continuous if you want it on the same page or Next Page if you want the names are on separate page with the form.
- Then in the Restrict Editing tab there will be a Select sections option show up. Click there and uncheck Section 1 (which is the section for names)

- Then when you enforce protection, you can add names in the section for names and your form still be protected
2- Use Read-only protection with content control
- If you want to use header, you can add a content control in the Header via Developer tab > Rich text content control (Aa)
- Then in Restrict editing, choose the Read-only option instead > select the content control and choose Everyone to allow all users add their name in there

- However, this option requires you to manually select all the checkboxes and check Everyone to add them into Exceptions so users will be able to check these boxes.
I hope this information is helpful. Please understand that our initial response does not resolve the issue immediately, but you can try these workarounds and let me know if it works for you.
Thank you for your patience and your understanding. If you have any questions or need further assistance, please feel free to share them in the comments so I can continue to support you.
I look forward to hearing from you.
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