Recompress an existing PDF using color detection in C#

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//We assume that GdPicture has been correctly installed and unlocked.
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GdPicturePDF oGdPicturePDF = new GdPicturePDF();
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oGdPicturePDF.SetCompressionForBitonalImage(PdfCompression.PdfCompressionJBIG2);
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oGdPicturePDF.SetCompressionForColorImage(PdfCompression.PdfCompressionJPEG);
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GdPictureImaging oGdPictureImaging = new GdPictureImaging();
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GdPictureStatus status = oGdPicturePDF.LoadFromFile("c:\\input.pdf", true);
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if (status == GdPictureStatus.OK)
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{
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   int PageCount = oGdPicturePDF.GetPageCount();
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   for (int Page = 1; Page <= PageCount; Page++)
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   {
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    oGdPicturePDF.SelectPage(Page);
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    for (int Image = 1; Image <= oGdPicturePDF.GetPageImageCount(); Image++)
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    {
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     int imageID = oGdPicturePDF.ExtractPageImage(Image);
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     if (oGdPicturePDF.GetStat() == GdPictureStatus.OK)
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     {
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      oGdPictureImaging.ColorDetection(imageID, true, true, true);
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      if (oGdPicturePDF.ReplaceImage(oGdPicturePDF.GetPageImageResName(Image - 1), imageID, false) != GdPictureStatus.OK)
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         MessageBox.Show("Error: " + status.ToString(), "Color Detection Example", MessageBoxButtons.OK, MessageBoxIcon.Error);
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      oGdPictureImaging.ReleaseGdPictureImage(imageID);
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     }
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     else
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      MessageBox.Show("Error: " + status.ToString(), "Color Detection Example", MessageBoxButtons.OK, MessageBoxIcon.Error);
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    }
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   }
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   status = oGdPicturePDF.SaveToFile("c:\\output.pdf", true);
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   if (status == GdPictureStatus.OK)
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    MessageBox.Show("Done!", "Color Detection Example", MessageBoxButtons.OK, MessageBoxIcon.Information);
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   else
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    MessageBox.Show("The PDF file can't be saved. Error: " + status.ToString(), "Color Detection Example", MessageBoxButtons.OK, MessageBoxIcon.Error);
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   oGdPicturePDF.CloseDocument();
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   oGdPictureImaging.Dispose();
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}
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else
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   MessageBox.Show("The PDF file can't be loaded. Error: " + status.ToString(), "Color Detection Example", MessageBoxButtons.OK, MessageBoxIcon.Error);
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oGdPicturePDF.Dispose();