How do we create a PDF which we password protect except for the signature and initals

We have an automated process which takes a Word document and converts it to a PDF.

We made the PDF password protected so the contract terms and conditions could not be altered.

We can't count on a specific location where the user will sign and/or initial the document because the document can contain 1 to x number of line items which can cause the document to be longer or shorter depending on that number of line items.

We still need the person to sign and initial the document.

How can we do this when we're creating the PDF dynamically from a Word document?