Check whether values of PDF form fields have been changed.

[Alex]

If you want to check whether values of PDF form fields have been changed, you need to do the following steps:

• Get and save information about field values before editing of PDF form.
• Get and compare information about field values when you want to determine changes in PDF form.

Here is C# code snippet that shows how to check whether values of PDF form fields have been changed:

Code: Select all

Dictionary<PdfTreeNodeBase, PdfBasicObject> _fieldValues;

/// <summary>
/// Checks whether values of PDF form fields have been changed.
/// </summary>
public void CheckFieldsAreChanged(PdfDocument document)
{
    Dictionary<PdfTreeNodeBase, PdfBasicObject> newFieldValues = GetFieldValues(document);
    if (_fieldValues != null)
    {
        if (AreFieldValuesChanged(_fieldValues, newFieldValues))
            MessageBox.Show("Changed");
    }
    _fieldValues = newFieldValues;
}

/// <summary>
/// Returns a value indicating whether values of PDF form fields have been changed.
/// </summary>
public static bool AreFieldValuesChanged(Dictionary<PdfTreeNodeBase, PdfBasicObject> fieldValues1, Dictionary<PdfTreeNodeBase, PdfBasicObject> fieldValues2)
{
    if (fieldValues1.Count != fieldValues2.Count)
        return true;
    foreach (PdfTreeNodeBase field in fieldValues1.Keys)
    {
        PdfBasicObject value1 = GetValue(fieldValues1[field]);
        if (!fieldValues2.ContainsKey(field))
            return true;
        PdfBasicObject value2 = GetValue(fieldValues2[field]);
        if (value1 == value2)
            continue;
        if (value1 == null || value2 == null)
            return true;
        if (value1.ToString() != value2.ToString())
            return true;
    }
    return false;
}

/// <summary>
/// Returns dictionary that contains values of PDF form fields.
/// </summary>
public static Dictionary<PdfTreeNodeBase, PdfBasicObject> GetFieldValues(PdfDocument document)
{
    Dictionary<PdfTreeNodeBase, PdfBasicObject> result = new Dictionary<PdfTreeNodeBase, PdfBasicObject>();
    if (document.InteractiveForm != null)
    {
        foreach (PdfInteractiveFormField field in document.InteractiveForm.GetTerminalFields())
        {
            result.Add(field, ((PdfDictionary)field.BasicObject)["V"]);
        }
    }
    return result;
}

/// <summary>
/// Returns value of PDF form field.
/// </summary>
private static PdfBasicObject GetValue(PdfBasicObject basicObject)
{
    if (basicObject is PdfIndirectReference indirectReference)
        return PdfIndirectObject.GetByReference(indirectReference).Value;
    return basicObject;
}