Answer
When creating a PDF form, there are times when you want to lock certain fields once someone has signed a signature field within the document. This can be done easily with Foxit PDF Editor!
1. With the form fields added to the PDF, right click on the Signature field you are wanting to edit and choose Properties. Then from the Signed tab, choose to “Mark as read-only” and select the fields you want to lock after signing. Finally, Close.
2. Sign the signature field!
3. After signing, the select fields will be flattened and locked to the PDF!