How do I save work on a created PDF so that I can continue to work on it or edit it later?

[Johnston5EA3]

I spent hours working on a PDF form and thought it was perfect.  Now that I have been using it, I can see changes I want to make to it.  Just clicking the "Edit PDF" tab does not allow me to edit to the degree I want or need.  I do not want to completely start over, I just want to get back into the "Create PDF" mode of the doc that I had when I originally created the form so that I can tweek it to be how I need it to be.  Is there a way to do that?

[Bernd Alheit]

When you want change the form use Tools > Prepare Form