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# Creating Auto-Calculating Form Fields

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Ever have the need to use a form that auto-calculates fields? Adobe Acrobat can do this for you just fine. Acrobat expert John Deubert shows you how to tell a form field to calculate its own value.
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A friend of mine has started a little company she runs from the comfort of her own home: She makes wake-up calls to people who don’t trust their alarm clocks (though why they’d trust her alarm clock, I couldn’t say). It’s not extremely profitable, but seems to keep her in beer money.

Every month, she bills her customers for services rendered using a PDF form, a simplified version of which is shown in Figure 1. It’s a straightforward form: how many wake-up calls, how much per call, and the final bill. The form’s only weakness is that it could be more than it is. The three “total” fields (labeled Wake-ups charge, Snoring surcharge, and Monthly Total in the figure) are just Text fields; my friend calculates the totals herself and enters them into the appropriate fields.

As it turns out, Acrobat can do calculations just as well as my friend can (better, maybe); in particular, it’s perfectly easy to have the totals fields calculate their own values.

That’s what we’re looking at in this article: How do you tell a form field to calculate its own value?

I should warn you that this is an intermediate topic; in particular, I assume you know how to create form fields on an Acrobat page. (You might take a look at the excellently written—why, yes, I did write it—Acrobat X Visual Quickstart Guide for an introduction to creating Acrobat forms.)

## Our Sample File

The sample file for this article, pictured in Figure 1, is a simple form that collects the number of wake-up events during a single month. Note that Acrobat highlights the form fields in blue so you can see them on the page; if this annoys you, you can turn it off by clicking the Highlight Existing Fields button at the top of the window (Figure 2).

As always, this file is available for downloading from http://www.acumentraining.com/resources.html; look for the file Auto-calculate.zip.

We’re going to turn three of the fields in this form into self-calculating fields: the Wake-up charge field, the Snoring surcharge field, and the Month’s Total field.

Let’s do it.