Hi
1.You can define a flag for your form. it is 1 by default. Then set a coditional formatting in the display setting for the btn1. the condition is : if flag is not equal to1 hide this button.
You should set a rule when you want to save or submit the form, to turn the flag back to its first value. I dont know how you want to close your form, if you are using a button to save, submit and close form, before all of this action define an action set this field values : set flag= 0 ). In this way the second time that form will be opend flag is not 1 so the btn1 is visible.
Ofcourse there are another ways... maybe you can use open and save rules, or role base views... but for all of them you need a flag to identify the state of your form.
2. I have a practical solution using SharePoint list. if you are using SharePoint Tell me To describe the solution.
hope to be useful for you dear friend!