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How to Add a Watermark to a PDF — Text, Opacity, Angle, and Code Guide

Add DRAFT, CONFIDENTIAL, or any custom text watermark to every page of a PDF. Control opacity, rotation, font size, and color. With code in pdf-lib, Python, and Ghostscript.

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Watermark PDF — add DRAFT, CONFIDENTIAL, or custom text watermark to every page

A draft report going to reviewers needs "DRAFT" stamped across every page. A confidential proposal needs "CONFIDENTIAL — DO NOT DISTRIBUTE" visible to anyone who opens it. A training document needs your company name repeated as a background to deter screenshot sharing.

Add a text watermark to any PDF for free with the ToolNest AI Watermark PDF tool — customize text, opacity, angle, color, font size, and position.

Watermark Options

OptionTypical valuesNotes
TextDRAFT, CONFIDENTIAL, SAMPLE, your nameAny text
Opacity20–50%Lower = more transparent
Rotation-45° to 45°Diagonal is harder to crop
ColorRed, gray, purple, blackDark colors on light PDFs
Font size36–96 ptLarger = more visible
PositionCenter, tileTiling repeats the watermark

Adding Watermarks in Code

JavaScript with pdf-lib

import { PDFDocument, rgb, StandardFonts, degrees } from 'pdf-lib';
import fs from 'fs';
 
async function addWatermark(inputPath, outputPath, options = {}) {
  const {
    text = 'CONFIDENTIAL',
    fontSize = 60,
    opacity = 0.3,
    angle = 45,             // degrees counterclockwise
    color = rgb(0.5, 0.2, 0.9),  // purple
  } = options;
 
  const pdfBytes = fs.readFileSync(inputPath);
  const pdfDoc = await PDFDocument.load(pdfBytes);
  const font = await pdfDoc.embedFont(StandardFonts.HelveticaBold);
  
  for (const page of pdfDoc.getPages()) {
    const { width, height } = page.getSize();
    const textWidth = font.widthOfTextAtSize(text, fontSize);
    
    page.drawText(text, {
      x: (width - textWidth) / 2,
      y: height / 2 - fontSize / 2,
      size: fontSize,
      font,
      color,
      opacity,
      rotate: degrees(angle),
    });
  }
  
  const newBytes = await pdfDoc.save();
  fs.writeFileSync(outputPath, newBytes);
}
 
await addWatermark('input.pdf', 'watermarked.pdf', {
  text: 'DRAFT',
  fontSize: 72,
  opacity: 0.25,
  angle: 45,
  color: rgb(0.8, 0.1, 0.1), // red
});

Python with pypdf + reportlab

from pypdf import PdfReader, PdfWriter
from reportlab.pdfgen import canvas
from reportlab.lib.colors import Color
import io, math
 
def create_watermark_page(width, height, text, font_size=60, angle=45, opacity=0.3, color=(0.5,0.2,0.9)):
    packet = io.BytesIO()
    c = canvas.Canvas(packet, pagesize=(width, height))
    c.setFont("Helvetica-Bold", font_size)
    c.setFillColor(Color(*color, alpha=opacity))
    c.translate(width / 2, height / 2)
    c.rotate(angle)
    text_width = c.stringWidth(text, "Helvetica-Bold", font_size)
    c.drawString(-text_width / 2, 0, text)
    c.save()
    packet.seek(0)
    return PdfReader(packet)
 
def add_watermark(input_path, output_path, text='CONFIDENTIAL', **kwargs):
    reader = PdfReader(input_path)
    writer = PdfWriter()
    
    for page in reader.pages:
        w = float(page.mediabox.width)
        h = float(page.mediabox.height)
        watermark = create_watermark_page(w, h, text, **kwargs)
        page.merge_page(watermark.pages[0])
        writer.add_page(page)
    
    with open(output_path, 'wb') as f:
        writer.write(f)
 
add_watermark('input.pdf', 'watermarked.pdf', 
              text='DRAFT', angle=45, opacity=0.25, font_size=72,
              color=(0.8, 0.1, 0.1))

Ghostscript

gs -dBATCH -dNOPAUSE -dSAFER \
   -sDEVICE=pdfwrite \
   -c "
     /watermark-dict <<
       /WatermarkText (CONFIDENTIAL)
       /Font /Helvetica-Bold
       /FontSize 60
       /GrayLevel 0.7
       /Angle 45
     >> def
   " \
   -f watermark.ps \
   -f input.pdf \
   -sOutputFile=watermarked.pdf

Frequently Asked Questions

Can a watermark be removed?

A text watermark added as a PDF text object (as pdf-lib and pypdf do) can theoretically be removed with PDF editing software, since it exists as a separate layer. For stronger protection, combine the watermark with flattening (rendering the page to an image first) or use password protection alongside the watermark.

Should the watermark be on top of the content or behind it?

For text documents, place the watermark behind the content (as a background layer) so the main text remains readable. For documents where the watermark must be clearly visible and hard to ignore, place it on top with 30–50% opacity. pdf-lib's drawText draws on top by default.

What font size should I use for watermarks?

For A4/Letter-size documents, 60–80pt bold text at 45° rotation typically looks professional. Too small (under 40pt) becomes hard to see. Too large (over 120pt) obscures the content.

Can I tile the watermark across the page?

Yes — instead of drawing one centered watermark, loop through a grid of positions and draw the text repeatedly:

for (let x = 0; x < width + 200; x += 250) {
  for (let y = 0; y < height + 200; y += 150) {
    page.drawText(text, { x, y, size: 30, font, color, opacity: 0.15, rotate: degrees(45) });
  }
}
Tags:#watermark PDF#add watermark PDF#CONFIDENTIAL PDF#DRAFT watermark#pdf-lib watermark#pypdf watermark

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ToolNest AI Team

The ToolNest AI team builds free tools that help developers, marketers, and creators do more online — faster.

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