Flatten PDF interactive form fields in C# and VB.NET

using System;
using SautinSoft.Pdf;
using System.IO;

class Program
{
	static void Main()
	{
		// This property is necessary only for licensed version.
		//SautinSoft.Pdf.Serial = "XXXXXXXXXXX";

		using (var document = PdfDocument.Load("FormFilled.pdf"))

		{
			// A flag specifying whether to construct appearance for all form fields in the document.
			bool needAppearances = document.Form.NeedAppearances;

			foreach (var field in document.Form.Fields)
			{
				// Do not flatten button fields.
				if (field.FieldType == PdfFieldType.Button)
				continue;

				// Construct appearance, if needed.
				if (needAppearances)
				field.Appearance.Refresh();

				// Get the field's appearance form.
				var fieldAppearance = field.Appearance.Get();

				// If the field doesn't have an appearance, skip it.
				if (fieldAppearance == null)
				continue;

				// Add a new content group to the field's page and
				// add new form content with the field's appearance form to the content group.
				// The content group is added so that transformation from the next statement is localized to the content group.
				var flattenedContent = field.Page.Content.Elements.AddGroup().Elements.AddForm(fieldAppearance);

				// Translate the form content to the same position on the page that the field is in.
				var fieldBounds = field.Bounds;
				flattenedContent.Transform = PdfMatrix.CreateTranslation(fieldBounds.Left, fieldBounds.Bottom);
			}

			// Remove all fields, thus making the document non-interactive,
			// since their appearance is now contained directly in the content of their pages.
			document.Form.Fields.Clear();

			document.Save("FormFlattened.pdf");
		}
	}
}