使用itext pdf的pdf上缺少彩色区域

Question

I am editing an existing pdf using itext pdf. While doing this, only a portion of rectangle box is showing as colored and some part is not highlighted. Looks like some overlay issue is happening here.

The yellow colour is not showing in complete rectangle.

    PdfContentByte canvas = stamper.getUnderContent(1);
    canvas.saveState();
    canvas.setColorFill(BaseColor.YELLOW);
    canvas.rectangle(36, 786, 66, 16);
    canvas.fill();
    canvas.restoreState();
    stamper.close();

Answer 1

To make your task work, you should not draw under the existing content (as so that content can simply cover your mark) but instead over it. And to make the original content shine through, you should use an appropriate blend mode:

PdfContentByte canvas = stamper.getOverContent(1);
canvas.saveState();
PdfGState state = new PdfGState();
state.setBlendMode(new PdfName("Multiply"));
canvas.setGState(state);
canvas.setColorFill(BaseColor.YELLOW);
canvas.rectangle(36, 786, 66, 16);
canvas.fill();
canvas.restoreState();
stamper.close();

( MarkContent test)

You didn't share your PDF, so I had to try with a PDF I have here. Using an appropriately changed rectangle position and size the code marks this

to look like this: