OCG layers

[ZingZing001]

Description

I developed a method for removing layered watermarks using Python, and surprisingly, this approach seemed to work at first, but after we had different people opening the processed PDF from different devices, things started to get weird.

Apple devices have no problem where the watermark stays hidden.
Android/Windows users still sees the watermark when they open the pdf.

Here's my remove layered pdf function in Python:

# Function to remove layer-based watermarks (OCGs)
def remove_layer_watermarks(file_path):
    try:
        doc = pymupdf.open(file_path)
        ocgs = doc.get_ocgs()  # Get the list of all Optional Content Groups (layers)
        print(ocgs)

        if ocgs:
          print("Found layers in the PDF.")
          for ocg in ocgs:
              names = ocgs[ocg]  # Get the details dictionary
              details = doc.xref_object(ocg, compressed=True)
              name = names.get('name', 'Unnamed Layer')  # Extract the 'name' field
              print(f"Layer xref: {ocg}, Name: {name}")
              
              if "watermark" in str(name).lower():
                print(f"Disabling watermark layer: {name}")
                doc.set_layer(-1, on=None, off=[ocg])
                
              elif "background" in str(name).lower():
                print(f"Disabling watermark layer: {name}")
                doc.set_layer(-1, on=None, off=[ocg])
                

        # Save the PDF with layer watermarks removed
        output_pdf_path = file_path.replace(".pdf", "_no_layer_watermark.pdf")
        doc.save(output_pdf_path)
        print("Layer watermarks removed. Modified PDF saved.")
  
        return output_pdf_path
    except Exception as e:
        print(f"Error: {e}")
        return None

I'm aware that this method only sets the water mark layer to invisible, where the layer still exists.

How to reproduce this issue

By running the function with a pdf as input, the pdf files got different oc layers.

PyMuPDF version

1.24.14

Operating system

MacOS

Python version

3.9