from PyPDF2 import PdfReader, PdfWriter

from reportlab.pdfgen import canvas

from reportlab.lib.pagesizes import letter,A0,A4,landscape

from decimal import Decimal

from pathlib import Path

from reportlab.pdfbase import pdfmetrics

from reportlab.lib.colors import Color, black, blue, red

from reportlab.pdfbase.ttfonts import TTFont

import io

import sys

import os

change xxx to your user name

sys.path.append(os.path.abspath("c:/users/xxxx/appdata/roaming/python/python310/site-packages"))

pdfmetrics.registerFont(TTFont('Vera', 'Vera.ttf'))

pdfmetrics.registerFont(TTFont('VeraBd', 'VeraBd.ttf'))

pdfmetrics.registerFont(TTFont('VeraIt', 'VeraIt.ttf'))

pdfmetrics.registerFont(TTFont('VeraBI', 'VeraBI.ttf'))

draw the text

listofpdfFiles=[]

put the pdf files to watermark on the same folder as the python script

def getPdfFiles():

root = "."  # take the current directory as root

for path in Path(root).glob("**/*.pdf"):
    listofpdfFiles.append(path)

def drawText(packet,width,height,text,textsize):

c = canvas.Canvas(packet, landscape(pagesize=A0))

c.saveState()

#c.setFillColorRGB(255, 0, 0) #choose your font colour
red50transparent = Color( 100, 0, 0, alpha=0.5)
black50transparent = Color( 0, 0, 0, alpha=0.5)
c.setFillColor(black50transparent)
#c.setFillColorRGB(255, 0, 0) #choose your font colour
c.setFont('Vera', textsize)

c.translate(width, height)

c.rotate(30)

c.drawString(0, 0, text)

c.restoreState()

c.save()

Function to add text to an existing PDF

def add_text_to_pdf(input_pdf, output_pdf, text):

# Read the existing PDF

reader = PdfReader(input_pdf, strict=False)

writer = PdfWriter()


# create a new PDF with Reportlab

packet = io.BytesIO()

packet.seek(0)


# read your existing PDF

existing_pdf = PdfReader(input_pdf, strict=False)

output = PdfWriter()


# add the "watermark" (which is the new pdf) on the existing page

for i in range(len(existing_pdf.pages)):

    page = reader.pages[i]

    width = float(page.mediabox.width)

    height = float(page.mediabox.height)

    # actual size of the pdf file

    lox = 0.5*float(page.mediabox.width)*25.4/72

    locy = 0.5*float(page.mediabox.height)*25.4/72

    print(width,height)
    #print(2*locx,2*locy)

    textsize=width/20 # text size relative to width of pdf
    textsize2=height/20
    print("textsize",textsize)
    faktor=3
    drawText(packet,0.5*width-faktor*textsize, 0.5*height-faktor*textsize2,text,textsize)

    new_pdf = PdfReader(packet)

    page = existing_pdf.pages[i]

    page.merge_page(new_pdf.pages[0])

    output.add_page(page)


# finally, write "output" to a real file

outputStream = open(output_pdf, "wb")
output.write(outputStream)
outputStream.close()

Example usage

getPdfFiles()

change the path to where your pdf files will be copied 'C:/Users/xxxx/Documents/pdfcopy/'

for fl in listofpdfFiles:

add_text_to_pdf(fl, 'C:/Users/xxxx/Documents/pdfcopy/'+fl.__str__(), "Vorläufige Plan")

print("finished")