final pdf = new PDFDocument();
final page = new PDFPage(pdf, pageFormat: new PDFPageFormat(PDFPageFormat.LETTER));
final g = page.getGraphics();
final font = new PDFFont(pdf);

g.setColor(new PDFColor(0.0, 1.0, 1.0));
g.drawRect(50.0, 30.0, 100.0, 50.0);
g.fillPath();

g.setColor(new PDFColor(0.3, 0.3, 0.3));
g.drawString(font, 12.0, "Hello World!", 50.0, 300.0);

var file = new File('file.pdf');
file.writeAsBytesSync(pdf.save());