try {
PdfWriter writer = PdfWriter.getInstance(document, new FileOutputStream("shading_pattern.pdf"));
document.open();
PdfShading shading = PdfShading.simpleAxial(writer, 100, 100, 400, 100, Color.red, Color.cyan);
PdfShadingPattern shadingPattern = new PdfShadingPattern(shading);
PdfContentByte cb = writer.getDirectContent();
BaseFont bf = BaseFont.createFont(BaseFont.TIMES_BOLD, BaseFont.WINANSI, false);
cb.setShadingFill(shadingPattern);
cb.beginText();
cb.setTextMatrix(100, 100);