Sum Total of Inputs

Acrobat provides 3 different calculation method and any one of the three is capable of summing four fields.

You can use the "Field is the _______ of the following fields" and select "Sum" and then select the fields to be included in the sum. Just use the mouse to highlight the field name and press the space bar.

You can use "Simplified field notation" and enter the field names separated by the "+" operator if the field names contain no special characters or spaces in their names.

And lastly you use the "Custom JavaScript calculation" to enter all the JavaScript commands to sum and set the field's value. Note the above 2 options also use JavaScript in the background to do their heavy scripting lifting at the loss of some control.

How to do (not so simple) form calculations by Thom Parker. Old but still relevant.

You don't need JS. Use this option in the Calculate tab and then select the fields you want to add up from the list: