documenso/packages/pdf/insertTextInPDF.ts

import fontkit from "@pdf-lib/fontkit";
import * as fs from "fs";
import { PDFDocument, StandardFonts, rgb } from "pdf-lib";

export async function insertTextInPDF(
  pdfAsBase64: string,
  text: string,
  positionX: number,
  positionY: number,
  page: number = 0,
  useHandwritingFont = true
): Promise<string> {
  const fontBytes = fs.readFileSync("public/fonts/Qwigley-Regular.ttf");

  const pdfDoc = await PDFDocument.load(pdfAsBase64);

  pdfDoc.registerFontkit(fontkit);

  const font = await pdfDoc.embedFont(useHandwritingFont ? fontBytes : StandardFonts.Helvetica);

  const pages = pdfDoc.getPages();
  const pdfPage = pages[page];

  const textSize = useHandwritingFont ? 50 : 15;
  const textWidth = font.widthOfTextAtSize(text, textSize);
  const textHeight = font.heightAtSize(textSize);
  const fieldSize = { width: 192, height: 64 };

  // Because pdf-lib use a bottom-left coordinate system, we need to invert the y position
  // we then center the text in the middle by adding half the height of the text
  // plus the height of the field and divide the result by 2
  const invertedYPosition =
    pdfPage.getHeight() - positionY - (fieldSize.height + textHeight / 2) / 2;

  // We center the text by adding the width of the field, subtracting the width of the text
  // and dividing the result by 2
  const centeredXPosition = positionX + (fieldSize.width - textWidth) / 2;

  pdfPage.drawText(text, {
    x: centeredXPosition,
    y: invertedYPosition,
    size: textSize,
    color: rgb(0, 0, 0),
    font,
  });

  const pdfAsUint8Array = await pdfDoc.save();
  return Buffer.from(pdfAsUint8Array).toString("base64");
}