Workaround for documents generated with PdfProcessing: When drawing lines using the FixedContentEditor the IsFilled graphic property should be set to false:

RadFixedDocument document = new RadFixedDocument();

Rect rect = new Rect(0, 0, 50, 50);
FixedContentEditor editor = new FixedContentEditor(document.Pages.AddPage());
editor.GraphicProperties.IsFilled = false;
editor.GraphicProperties.IsStroked = true;

editor.Position.Translate(50, 50);
editor.GraphicProperties.StrokeColor = new RgbColor(255, 0, 0);
editor.DrawText("Lines");
editor.DrawLine(rect.TopLeft, rect.TopRight);
editor.DrawLine(rect.TopRight, rect.BottomRight);
editor.DrawLine(rect.BottomRight, rect.BottomLeft);
editor.DrawLine(rect.BottomLeft, rect.TopLeft);