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Mofumi PDF

Form Logic Designer

Beta

Add calculations, validation and show/hide rules to PDF forms with simple one-line rules.

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About this tool

Form Logic Designer adds behaviour to fillable PDFs without writing JavaScript. Write one rule per line and Mofumi converts it into the form actions that Adobe Acrobat and Reader understand. The field names of your form are listed at the top when you open the file.

Rules: “total = sum(a, b, c)” (also product, avg, min, max), arithmetic such as “vat = subtotal * 0.07”, “validate age 0..120 : message”, “show details when agree”, “hide note when country = Japan”, “required name” and “format total number 2”. Lines starting with # are comments.

This tool is in beta. The logic runs in viewers that support form JavaScript (Acrobat, Foxit, many mobile apps); browser built-in viewers usually ignore it. Mofumi itself never runs PDF JavaScript.

Engines: pdf-lib

How to use

  1. 1

    Open a fillable PDF (make one with Form Creator).

  2. 2

    Write your rules, one per line.

  3. 3

    Click “Add form logic” and download.

Use cases

  • Order forms

    Calculate line totals, VAT and the grand total automatically.

  • Validated applications

    Reject impossible ages or amounts with a friendly message.

  • Conditional sections

    Show extra fields only when a checkbox is ticked.

Frequently asked questions

Why doesn't the calculation work in my browser?

Most browser viewers don't run form scripts. Open the file in Adobe Acrobat Reader.

How do I find field names?

They are listed as comments at the top of the rules box when you open the file.

Can I combine rules on one field?

Yes, a field can have a calculation, validation and a show/hide rule.

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