ABCpdf .NET PDF Component Documentation - OpAtom Find Function. Finds specified types of OpAtom entries in an array.

This example shows how to use the Array.FromContentStream function to parse a content stream and then use the Find method to search for certain types of color operators and replace them with other color operators. In this example this has the effect of converting some black parts of the PDF to red. For a more comprehensive approach one would use the ContentStreamOperation class to determine all content streams associated with the pages in question.

using (Doc doc = new Doc()) {
  doc.Read(Server.MapPath("spaceshuttle.pdf"));
  doc.RemapPages(new int[] { 1, 1 });
  doc.PageNumber = 2;
  Page page = doc.ObjectSoup[doc.Page] as Page;
  StreamObject[] layers = page.GetLayers();
  MemoryStream st = new MemoryStream();
  foreach (StreamObject layer in layers) {
    if (!layer.Decompress())
      throw new Exception("Unable to decompress stream.");
    byte[] data = layer.GetData();
    st.Write(data, 0, data.Length);
    layer.CompressFlate();
  }
  ArrayAtom array = ArrayAtom.FromContentStream(st.ToArray());
  if (true) {
    var items = OpAtom.Find(array, new string[] { "k" });
    foreach (var pair in items) { // make red
      Atom[] args = OpAtom.GetParameters(array, pair.Item2);
      if (args != null) {
        ((NumAtom)args[0]).Real = 0;
        ((NumAtom)args[1]).Real = 1;
        ((NumAtom)args[2]).Real = 1;
        ((NumAtom)args[3]).Real = 0;
      }
    }
  }
  if (true) {
    var items = OpAtom.Find(array, new string[] { "rg" });
    foreach (var pair in items) { // make green
      Atom[] args = OpAtom.GetParameters(array, pair.Item2);
      if (args != null) {
        ((NumAtom)args[0]).Real = 0;
        ((NumAtom)args[1]).Real = 1;
        ((NumAtom)args[2]).Real = 0;
      }
    }
  }
  byte[] arrayData = array.GetData();
  StreamObject so = new StreamObject(doc.ObjectSoup);
  so.SetData(arrayData, 1, arrayData.Length - 2);
  doc.SetInfo(page.ID, "/Contents:Del", "");
  page.AddLayer(so);
  doc.Save(Server.MapPath("ReplaceColors.pdf"));
}

Using doc As New Doc()
  doc.Read(Server.MapPath("spaceshuttle.pdf"))
  doc.RemapPages(New Integer() {1, 1})
  doc.PageNumber = 2
  Dim page As Page = TryCast(doc.ObjectSoup(doc.Page), Page)
  Dim layers As StreamObject() = page.GetLayers()
  Dim st As New MemoryStream()
  For Each layer As StreamObject In layers
    If Not layer.Decompress() Then
      Throw New Exception("Unable to decompress stream.")
    End If
    Dim data As Byte() = layer.GetData()
    st.Write(data, 0, data.Length)
    layer.CompressFlate()
  Next
  Dim array As ArrayAtom = ArrayAtom.FromContentStream(st.ToArray())
  If True Then
    Dim items = OpAtom.Find(array, New String() {"k"})
    For Each pair As var In items
      ' make red
      Dim args As Atom() = OpAtom.GetParameters(array, pair.Item2)
      If args <> Nothing Then
        DirectCast(args(0), NumAtom).Real = 0
        DirectCast(args(1), NumAtom).Real = 1
        DirectCast(args(2), NumAtom).Real = 1
        DirectCast(args(3), NumAtom).Real = 0
      End If
    Next
  End If
  If True Then
    Dim items = OpAtom.Find(array, New String() {"rg"})
    For Each pair As var In items
      ' make green
      Dim args As Atom() = OpAtom.GetParameters(array, pair.Item2)
      If args <> Nothing Then
        DirectCast(args(0), NumAtom).Real = 0
        DirectCast(args(1), NumAtom).Real = 1
        DirectCast(args(2), NumAtom).Real = 0
      End If
    Next
  End If
  Dim arrayData As Byte() = array.GetData()
  Dim so As New StreamObject(doc.ObjectSoup)
  so.SetData(arrayData, 1, arrayData.Length - 2)
  doc.SetInfo(page.ID, "/Contents:Del", "")
  page.AddLayer(so)
  doc.Save(Server.MapPath("ReplaceColors.pdf"))
End Using