Hi Chrisk,
Sorry for the delay in response.
As you need to keep the format stable for the text form field when sending the form for signature, please try to set the validation for that particular field.
For example: if you have created a text field for adding the US currency, refer the steps shown below:
- Double click on the text form field to open the Text field properties box.
- Then select "Currency" from the drop-down of Validation.
- Select the Country and Value range if you wish to add any.
- Click "OK" at the bottom of that window.

Hope that answers your query.
Let us know if you have any question or you referring to something else.
Regards,
Meenakshi