PDF allows the creation of interactive forms. Sometimes you will hear these types of PDF referred to as electronic forms, eForms or AcroForms.

To a client an eForm simply looks like a normal PDF containing text boxes, buttons and other interactive elements of the type you typically see on the web.

Indeed eForms support elements almost identical to HTML forms. They also support mechanisms very similar or identical to HTML forms for content submission to a web server.

For more details see the Adobe Technical Training: eForms pages.

Most people coming to eForms will be coming from an HTML background.There are subtle differences between the PDF form model and the HTML form model that can cause confusion.

In HTML a form is part of a web page. Each field in the HTML form has a visible appearance on the page (with the exception of hidden fields). So the concept of a field and what it looks like on the page is pretty much identical.

eForms separate the idea of a field from its visible representation.

Each page of the document owns a set of visible annotations. There are lots of different types of annotation but the ones that are used in eForm fields are called widgets. A widget contains properties that allow a PDF reader to display it appropriately on the page.

Each document owns a tree structure of fields which spans the entire document. Each field has a name and also a full name (like a file path) which tells you how to get to that field from the top level of the tree. The leaves of the tree contain the visible widgets that you see on the pages. Note that PDF does not require that full names are unique.

So there are two independent sets of entities each with its own features. The bits you see and which people normally call fields are in fact widgets.

Widgets don't have a name or identity as such - it's just that they may be associated with a field which has an identity. Similarly a field doesn't exist at a location or on a page it is just that it is associated with a widget that exists at a particular location on a particular page.

ABCpdf hides these distinctions from you. When you ask for a field by name it will return you the widget associated with that field. Given the widget you can find out where it is physically located in terms of page numbers and page rectangles. Similarly if you have a widget you can ask it for a field name. Behind the scenes ABCpdf finds the field associated with the widget and returns you the field name.

So why are eForms useful? There are a range of purposes to which eForms can be put. However probably the most common purpose is to provide placeholders in template PDFs.

Suppose you have a template document you want to use within ABCpdf. Using Acrobat you can insert form fields into the PDF at locations you want content to be inserted. Using ABCpdf you can automatically detect the locations of those fields and enter content at those locations.

If later you want to shift your content a little it's a simple matter to open the PDF in Acrobat and move the fields around.

See the eForm Example for details.