1. Download and install ImageMagick + Convert Module
2. Execute the following command in the console

$ convert -density 200 INPUT.pdf -rotate 0.3 +noise Multiplicative -format pdf  -quality 85 -compress JPEG -colorspace gray OUTPUT.pdf

• -density: set the input DPI to 200
• -rotate: set Page rotation to 0.3 degrees
• +noise: add noise to the PDF (other Noise-Options: https://www.imagemagick.org/script/command-line-options.php#noise)
• -format: set format to PDF for the correct sizing (A4)
• -quality: set JPEG Quality to 85%
• -compress: set compress to jpeg (other Compress-Options: https://www.imagemagick.org/script/command-line-options.php#compress)
• -colorspace: set color to gray

from __future__ import print_function
import os
import subprocess

input_dir = "Input/"
output_dir = "Output/"

if not os.path.exists(output_dir):
    os.makedirs(output_dir)
for root, dirs, files in os.walk(input_dir):
    for file in files:
        if file.endswith(".pdf"):
            input_filename = os.path.join(root, file)
            print ("Process: " + input_filename)
            p = subprocess.Popen(
              'convert -density 200 '+input_filename+' -rotate 0.3 +noise Multiplicative -format pdf -quality 85 -compress JPEG -colorspace gray '+str(output_dir +  file), shell=True)