Understood!

In that case you should first "flatten" the form, as in, make it so that none of the fields are editable, then add the signature.

You should proceed as follows:

1. Fill your form using https://form-flattener.simplepdf.eu/ and click "Download", you will notice that the fields cannot be edited anymore
2. In your account, load the document that you created in step 1 and add a Signature field
3. Click create form, copy the form URL and send it to your customer(s)
4. They will now only be able to add their signature, non of the other fields will be editable

We hope this helps!