How PDF forms use JavaScript for validation

This blog post assumes you are aware of PDF forms. If this is a new topic for you, check out our introductory blog post . PDF forms are able to utilise JavaScript as a dynamic way to get the form to include actions and perform calculations. Need to make sure a field only allows the user to input a number? You can do that. Want the next field to pre-populate depending on what option the user selected? You can do that too. In this post, I want to discuss how PDF forms can use JavaScript for validation. AcroForms To start with, I’ll discuss the different ways that an AcroForms file might allow for validation of the PDF. The main method that an AcroForms file will validate fields is defined in the fields’ additional-actions (AA) entry. This is a dictionary where you can define behaviour to happen at specific triggers/events. For form validation, the most relevant of these events are: Bl K V Bl (Uppercase B, Lowercase L) The Bl event is triggered when an annotation loses the input focus. Th