PDF form actions on Android

A PDF action is similar to a web hyperlink, but it’s much more flexible. Nutrient supports most common actions defined in Adobe’s PDF Reference (page 417ff).

The most common types are GoTo and URI. However, many documents also use named actions for page changes.

Every Action subclass can be parsed from a PDF:

Action	Nutrient class	Use case
GoTo	`GoToAction`	Go to a destination (page) in the current document.
URI	`UriAction`	Resolve a uniform resource identifier (web link).
Hide	`HideAction`	Set an annotation’s hidden flag.
Named	`NamedAction`	Execute an action predefined by the conforming reader.
SubmitForm	`SubmitFormAction`	Submit form data.
ResetForm	`ResetFormAction`	Set fields to their default values.
JavaScript	`JavaScriptAction`	Execute a JavaScript script.

Actions are chainable via the getSubActions property. Certain annotations, such as the LinkAnnotation and the WidgetAnnotation, can contain an action. An OutlineElement also contains an action; as such, it supports the same types of actions as an annotation (for example, a PDF outline can open a web link).

Trigger events

WidgetAnnotation can contain a set of additional actions on top of the standard action described above. Each of these additional actions is tied to a specific AnnotationTriggerEvent.

All trigger events can be parsed from a PDF. However, Nutrient only supports action execution for a subset of these events (unsupported events are ignored):

Event	Use case
`MOUSE_DOWN`	Action to be executed when touching down on an annotation.
`MOUSE_UP`	Action to be executed when touching up after a successful tap gesture on an annotation.
`RECEIVE_FOCUS`	Action to be executed when an annotation gets selected.
`LOOSE_FOCUS`	Action to be executed when an annotation gets deselected.
`FORM_CHANGED`	A JavaScript action to be executed when a user types a keystroke into text or combo box fields or modifies selected options in list box fields. The action can reject or modify the keystroke.
`FIELD_FORMAT`	A JavaScript action to be executed before the form field is formatted.
`FORM_VALIDATE`	A JavaScript action to be executed when the form field’s value is changed. This is used to check whether the new value is valid.
`FORM_CALCULATE`	A JavaScript action to be executed to recalculate the value of this form field when another field changes.

ℹ️ Note: To stay backward compatible with older PDF specifications, Nutrient will give annotation actions returned by getAction() precedence over an additional MOUSE_UP action.

ℹ️ Note: Trigger events specific to form fields (FORM_CHANGED, FIELD_FORMAT, FORM_VALIDATE, and FORM_CALCULATE) only support JavaScriptAction.

Executing actions

You can use PdfFragment#executeAction to execute PDF actions:

annotation.action?.let { action ->
  fragment.executeAction(action)
}

if (annotation.getAction() != null) {
  fragment.executeAction(annotation.getAction());
}

You can also provide an optional ActionSender to inform the action executor about the context in which it should execute the action:

formElement.annotation.action?.let { action ->
  fragment.executeAction(action, ActionSender(formElement))
}

WidgetAnnotation annotation = formElement.getAnnotation();
if (annotation.action != null) {
  fragment.executeAction(annotation.action, new ActionSender(formElement));
}

You must provide ActionSender when executing JavaScriptAction. This way, you’ll provide the correct execution context to the action executor. If you don’t provide the action sender in this case, your JavaScript scripts will be executed as document-level scripts instead. This means that you won’t be able to format or validate form fields, nor will you be able to access form fields or annotations via the this object in your scripts.

ℹ️ Note: The file structure for the action has to be correctly specified for it to work. The files in question should be in a local folder.