Add watermark to pdf java iText

Question

I want to add a image or text watermark to pdf file. I found some examples online, but my case is a little bit different.

I have an existing pdf template which is already populated with dynamic data and converted to byte[]. This generated bytes are later exported to pdf.

I would like to add the watermark to that generated bytes. Something like:

byte[] addWatermark(byte[] generatedBytes){
  byte[] bytesWithWatermark;

  //add watermark to bytes

  return bytesWithWatermark;
}

I just can't seem to figure out how to do this with iText.

Just feed the byte[] into a stream and use that stream to feed into a PdfReader. Create a PdfStamper with a different byte output stream, apply watermark using the example you found and return the bytes from the outputstream after closing the PdfStamper — Samuel Huylebroeck

mkl mkl · Accepted Answer · 2017-10-19T09:25:14

You say you already have examples for applying watermarks using iText. As you already have a PDF, you should use code from an example that adds watermarks to existing PDFs. This should be an example that works with a PdfReader / PdfStamper pair, e.g. those here, which all have the structure

PdfReader reader = new PdfReader(SOME_SOURCE);
PdfStamper stamper = new PdfStamper(reader, SOME_TARGET_STREAM);
[... add watermark to all pages in stamper ...]
stamper.close();
reader.close();

To make these example fit into your addWatermark method, simply use your byte[] instead of SOME_SOURCE and a ByteArrayOutputStream instead of SOME_TARGET_STREAM:

byte[] addWatermark(byte[] generatedBytes) {
    try (ByteArrayOutputStream target  = new ByteArrayOutputStream()) {
        PdfReader reader = new PdfReader(generatedBytes);
        PdfStamper stamper = new PdfStamper(reader, target);
        [... add watermark to all pages in stamper ...]
        stamper.close();
        reader.close();
        return target.toByteArray();
    }
}

PS As you used only the tag itext and not the tag itext7, I assumed you were looking for a solution for iText 5.5.x. But the same principle as applied here, i.e. using your byte[] as source argument and a ByteArrayOutputStream as target argument, will also allow you to make iText 7.x examples fit into your method frame.

Add watermark to pdf java iText

1 Answers