Static PDF Form Conversion with C# and .NET

PDF interactive form flattening is the process of making a PDF document non-interactive by taking the appearance of form fields, incorporating their appearance into the static contents of the PDF page containing them, and finally removing the form fields.

In the realm of digital document management, interactive PDF forms are a powerful tool for collecting data. However, there are scenarios where you might need to convert these interactive forms into a static format. This process is known as "flattening" PDF forms. Flattening a PDF form means converting the interactive form fields into static content, making the document non-interactive. This article will guide you through the process of flattening PDF interactive form fields using C# and .NET with the help of the SautinSoft PDF.Net library.

Pay attention to what the smoothing of interactive forms is for:

  • Data Integrity: Flattening ensures that the data entered into the form fields cannot be altered.
  • Compatibility: Flattened PDFs are more compatible with various PDF viewers and printers.
  • Security: Reduces the risk of form data being tampered with.
  • Archiving: Ideal for archiving documents where the form data needs to be preserved in a static format.

Step-by-Step Guide:

  1. Add SautinSoft.PDF from NuGet.
  2. Load the PDF Document.
  3. Flattening the Form Fields.
  4. Save the PDF Document.

Input file:

Output result:

Полный код

using System;
using System.IO;
using SautinSoft;
using SautinSoft.Pdf;
using SautinSoft.Pdf.Content;
using SautinSoft.Pdf.Forms;

namespace Sample
{
    class Sample
    {
        /// <summary>
        /// Fill in PDF interactive forms.
        /// </summary>
        /// <remarks>
        /// Details: https://sautinsoft.com/products/pdf/help/net/developer-guide/flatten-interactive-forms.php
        /// </remarks>
        static void Main(string[] args)
        {
            // Before starting this example, please get a free 100-day trial key:
            // https://sautinsoft.com/start-for-free/

            // Apply the key here:
            // PdfDocument.SetLicense("...");

            string pdfFile = Path.GetFullPath(@"..\..\..\FormFilled.pdf");

            using (var document = PdfDocument.Load(pdfFile))
            {
                // 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");
            }

            System.Diagnostics.Process.Start(new System.Diagnostics.ProcessStartInfo("FormFlattened.pdf") { UseShellExecute = true });
        }
    }
}

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Option Infer On

Imports System
Imports System.IO
Imports SautinSoft
Imports SautinSoft.Pdf
Imports SautinSoft.Pdf.Content
Imports SautinSoft.Pdf.Forms

Namespace Sample
	Friend Class Sample
		''' <summary>
		''' Fill in PDF interactive forms.
		''' </summary>
		''' <remarks>
		''' Details: https://sautinsoft.com/products/pdf/help/net/developer-guide/flatten-interactive-forms.php
		''' </remarks>
		Shared Sub Main(ByVal args() As String)
			' Before starting this example, please get a free 100-day trial key:
			' https://sautinsoft.com/start-for-free/

			' Apply the key here:
			' PdfDocument.SetLicense("...");

			Dim pdfFile As String = Path.GetFullPath("..\..\..\FormFilled.pdf")

			Using document = PdfDocument.Load(pdfFile)
				' A flag specifying whether to construct appearance for all form fields in the document.
				Dim needAppearances As Boolean = document.Form.NeedAppearances

				For Each field In document.Form.Fields
					' Do not flatten button fields.
					If field.FieldType = PdfFieldType.Button Then
						Continue For
					End If

					' Construct appearance, if needed.
					If needAppearances Then
						field.Appearance.Refresh()
					End If

					' Get the field's appearance form.
					Dim fieldAppearance = field.Appearance.Get()

					' If the field doesn't have an appearance, skip it.
					If fieldAppearance Is Nothing Then
						Continue For
					End If

					' 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.
					Dim 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.
					Dim fieldBounds = field.Bounds
					flattenedContent.Transform = PdfMatrix.CreateTranslation(fieldBounds.Left, fieldBounds.Bottom)
				Next field

				' 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")
			End Using

			System.Diagnostics.Process.Start(New System.Diagnostics.ProcessStartInfo("FormFlattened.pdf") With {.UseShellExecute = True})
		End Sub
	End Class
End Namespace

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