Selective Flattening of Form Fields Using ABCpdf

Let’s assume you have a form with a lot of form fields, and somewhere during your forms workflow, you want to flatten some fields to “burn in” the information and convert it from an interactive field to static PDF content. There are different ways to accomplish this. One option is to do this all in Acrobat’s JavaScript. Unfortunately, when you lookup the documentation for the Doc.flattenPages() method, it does not talk about selecting only a subset of fields (unless these fields are all on one specific page, and that page does not contain any fields that should not be flattened). But, there is an optional parameter that allows us to specify what should happen to fields that are set to only be displayed in the viewer, but not be printed: The “nNonPrint” parameter, when set to the numeric value “1”, will leave
these fields alone, and will not flatten them (a value of “0” will flatten them and a value of “2” will remove them from the document).

This allows us to modify the document before we call the Doc.flattenPages() method: If we turn all fields that should not be flattened into non-printing fields, then flatten the document, and then in a last step reverse that first change, we can do flatten only a subset of fields. The problem gets a bit more complex when we already have non-printing fields in the document that we want to remain non-printing, or if we have non-printing fields that we want to flatten. That will require quite a bit of logic to save the original state of all fields, turn those fields we want to flatten into printing form fields, turn the fields that we don’t want to flatten into non-printing fields, flatten the document, and then restore the original settings again. As I said, a bit complex.

As long as we don’t need to do this within Acrobat, there is another solution: The ABCpdf library that I’ve mentioned before provides functionality to flatten fields on a per-field basis. [ Full disclosure: The fine folks at webSupergoo provided me with a free license to ABCpdf 8 based on that old blog post. That’s what I am still using for my experiments. They are up to version 10 by now, and based on their feature comparison chart, there are a few new features in this version that sound interesting. ]

Now, when you search for “flattening” in the ABCpdf manual, you won’t find anything that will help you in this case: The only flattening I found in my version is for flattening layers, and versions 9 and 10 support transparency flattening. Nothing about form fields. It took me a bit of head scratching and exploring the Form and Field APIs to figure out that form or field flattening is actually done via a process called “stamping”. Once that hurdle was cleared, it was pretty simple to come with a routine to flatten just one field at a time. Here is the VB code I’ve used (the same will also work in C# or via any of the other interfaces that ABCpdf supports):

' This assumes that we already have an open document 'theDoc'
Dim theField As Field

' set the field 'Text1' to some value
theField = theDoc.Form.Fields("Text1")
theField.Value = "Some value"

' flatten one form field

' flatten all form fields in the document

Just to demonstrate how to flatten a whole document, I’ve added that as the last line in this snippet.

This makes it very simple to e.g. define an array of field names to be flattened, and then just loop over that array, get the field, and flatten one at a time.

This feature in ABCpdf is very useful, and easy to use – even though it has a name that is a bit confusing to somebody who works with a different kind of PDF Stamps on a regular basis 🙂

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