Thanks for reaching out to Jotform Support. Do you mean to change the size of the fields added to the smart PDF form? If so, you can do this by customizing the form designer settings that can be accessed by clicking the roller icon located on the right side of the page:
If that’s not exactly what you’re looking for, could you please give us an example in a screenshot so we can understand the requirement and respond accordingly? This guidewill show you how to do that.
Let us know if there’s anything else we can help you with.