If you want to disable the merchant from modifying specific PDF fields when e-signing a PDF application, then you will need to edit the PDF file and configure such fields to be read-only fields.

Additionally, you may also configure specific fields to be required (for example the signature fields, initials fields, etc.). 

To update your PDF application follow these steps:

1. Go to Manage > Administration > E-Signature > Import PDFs, download the desired PDF application, and open it in Adobe Acrobat Pro.

2. In Adobe Acrobat Pro, go to View > Tools > Prepare Form > Open (depending on your version of Acrobat, the PDF form editing menu may be accessed in a different way).

3. Right-click on the field that you wish to edit, and click Properties:

4. On the General tab, check or uncheck the Read Only and the Required properties as needed:

Note: Make sure that you don't make set the initials or the signature fields as Read-Only (or any other field that the merchant should fill in). Typically, the pricing fields are marked as Read-Only, and the fields that must be filled in (such as business name, contact info, and similar) are marked as Required.

5. After you have updated your PDF file, save your changes and upload the PDF file back to the same application from which you first downloaded the PDF (in step 1). New applications sent out from that point forward will show the updated set of Read-Only and Required fields to the merchant.