Cannot edit PDFs created in Word: "You cannot edit this file as a form due to its security settings"

I'm using Word 2019 which is up-to-date and Adobe Acrobat CC which is up-to-date (23.003.20215).

I created a form as a Word document, saved it as a PDF, opened it in Acrobat, clicked "Prepare form", selected to create the form from the open file and I get the error, "You cannot edit this file as a form due to its security settings".

When I go to Menu > Protections > Security properties in Acrobat, it says, "Security Method: No Security".

I have used File > Save As and chosen "PDF (*.pdf)" and I get the error.

I have used the "Save as Adobe PDF" option in Word and I get the error.

I have printed the document to the "Adobe PDF" printer and I get the error.

I have converted it to a JPEG and back to a PDF and I get the error.

I have opened the .docx file in the prepare form wizard and I get the error.

When I look at the .docx properties there is no document protection. I'm the author of the document.

I can't prepare any PDFs I save from Word. WHY?