title: Add background watermark to pdf files via PHP for existing .pdf files?
body: <p>I have a request from a client which requires me to process pdf files they upload. They upload pdf files and I search the pdf files for certain patterns and am supposed to add specific watermarks under certain conditions. Is there a way via php to open a pdf file, and add the background image and save it upon uploading?</p>
  
  <p>Example:
  Uploaded pdf file contains the word "Hello".. (add a smiley face background to pdf pages)</p>
  
  <p>Uploaded pdd file contains "hey!" (add company logo as background for pdf pages)</p>
  
  <p>Greatly appreciate your input! Thank you.</p>