A problem with custom formulas in text forms

[altrealt]

Hey there, can you, guys please tell me how to refer to already existing text forms in javascript in order to write my own javascript formula wich will basicly take the number from one text form, multiply it by 2, add '+' to it and the result will be displayed in the other form?

[lyndi_wu]

altrealt

If you have the sample pdf form with Javascript , you can get Javascript in text filed properties or Document Javascript, you get and refer to if you know the JS.