Add checkbox or radio button to pdf template with HTML Source Editor and it is erased when saving.

Hi, when I try to add a chekbox to any pdf template with HTML Source Editor and it is updated, the checkbox appears in the template, but when saving the template, the checkbox is erased from the template and the HTML code.

I check the directory permissions, quick repair and rebuild, update from 7.10.2 to 7.10.7 version, but the fault is not corrected.

I’ve searched for a solution in the forum but nothing fixes it.

Thanks.