PDF Annotation not visible on Image using pdfbox A

Question

I have text annotation on my pdf but when I am converting pdf to image file using pdfbox api, annotation disappears(not visible on image). I have searched for couple of forums but I did not get accurate answer of this question.

for (int page = 0; page < document.getNumberOfPages(); ++page) {
    BufferedImage bim = pdfRenderer.renderImageWithDPI(page,70,ImageType.RGB);

    // suffix in filename will be used as the file format
    ImageIOUtil.writeImage(bim, pdfFullPath + "-" + (page+1) + ".png", 70);
}

Creating Text annotation like below

//generate instanse for annotation
PDAnnotationTextMarkup txtMark = new PDAnnotationTextMarkup(PDAnnotationTextMarkup.SUB_TYPE_FREETEXT);

Some of the forums, I have read that one need to set Appearance to above object. But how I need to set appearance object to make annotation visible on my image.

Any help is greatly appriciated