Pythonで既存PDFにSVGの透かしを追加する

python -m venv .venv
source .venv/bin/activate
python -m pip install svglib==2.2.0 reportlab==4.4.9 pypdf==6.10.0

from io import BytesIO
from pathlib import Path
 
from pypdf import PdfReader, PdfWriter, Transformation
from pypdf.generic import RectangleObject
from reportlab.graphics import renderPDF
from reportlab.lib.colors import HexColor
from reportlab.pdfgen import canvas
from svglib.svglib import svg2rlg
 
SVG = '''<svg xmlns="http://www.w3.org/2000/svg" width="240" height="80"
             viewBox="0 0 240 80">
  <path fill="#315d6f" fill-opacity="0.25" fill-rule="nonzero"
        d="M10 60 L45 8 L80 60 Z M31 48 L59 48 L45 27 Z"/>
  <path fill="#315d6f" fill-opacity="0.25"
        d="M95 23 H216 V31 H95 Z M95 39 H190 V47 H95 Z
           M95 55 H205 V63 H95 Z"/>
</svg>'''
 
 
def make_demo_source(destination):
    stream = BytesIO()
    document = canvas.Canvas(stream, pagesize=(420, 300))
    specifications = [
        (420, 300, '#f5eddb', 'SOURCE PAGE ONE'),
        (300, 420, '#ffffff', 'SOURCE PAGE TWO'),
        (360, 260, '#e8eef0', 'SOURCE PAGE THREE')
    ]
    for width, height, background, label in specifications:
        document.setPageSize((width, height))
        document.setFillColor(HexColor(background))
        document.rect(0, 0, width, height, fill=1, stroke=0)
        document.setFillColor(HexColor('#183a42'))
        document.setFont('Helvetica-Bold', 16)
        document.drawString(28, height - 40, label)
        document.setFont('Helvetica', 10)
        document.drawString(28, height - 62, 'Original text remains in the PDF content.')
        document.drawString(28, 28, 'Original vector line and opaque page background')
        document.setStrokeColor(HexColor('#c47b44'))
        document.setLineWidth(3)
        document.line(28, 48, width - 28, 48)
        document.showPage()
    document.save()
    reader = PdfReader(stream)
    reader.pages[1].cropbox = RectangleObject([10, 20, 290, 400])
    reader.pages[2].rotate(90)
    writer = PdfWriter()
    for page in reader.pages:
        writer.add_page(page)
    writer.write(destination)
 
 
def make_overlay(svg_path, width, height):
    drawing = svg2rlg(str(svg_path))
    if drawing is None or drawing.width <= 0 or drawing.height <= 0:
        raise ValueError('The SVG did not produce a usable drawing')
    scale = width * 0.65 / drawing.width
    left = (width - drawing.width * scale) / 2
    bottom = (height - drawing.height * scale) / 2
    drawing.scale(scale, scale)
    stream = BytesIO()
    overlay = canvas.Canvas(stream, pagesize=(width, height))
    renderPDF.draw(drawing, overlay, left, bottom)
    overlay.save()
    return PdfReader(stream).pages[0]
 
 
def add_artwork(source_path, svg_path, output_path, *, over):
    reader = PdfReader(source_path)
    if reader.is_encrypted:
        raise ValueError('Encrypted inputs are outside this example')
    if reader.get_fields():
        raise ValueError('Form handling is outside this example')
    writer = PdfWriter()
    writer.clone_document_from_reader(reader)
    # Cloning in pypdf 6.10.0 does not retain the source header version.
    # This overlay uses transparency, introduced in PDF 1.4.
    writer.pdf_header = max(reader.pdf_header, '%PDF-1.4')
    for page in writer.pages:
        if page.rotation:
            page.transfer_rotation_to_content()
        box = page.cropbox
        width, height = float(box.width), float(box.height)
        overlay = make_overlay(svg_path, width, height)
        page.merge_transformed_page(
            overlay,
            Transformation().translate(float(box.left), float(box.bottom)),
            over=over,
            expand=False
        )
    writer.write(output_path)
 
 
if __name__ == '__main__':
    output = Path('watermark-output')
    output.mkdir(exist_ok=True)
    artwork = output / 'emblem.svg'
    artwork.write_text(SVG)
    source = output / 'source.pdf'
    make_demo_source(source)
    add_artwork(source, artwork, output / 'overlay-top.pdf', over=True)
    add_artwork(source, artwork, output / 'underlay.pdf', over=False)

python watermark_demo.py

add_artwork(
    Path("original.pdf"),
    Path("emblem.svg"),
    Path("watermarked.pdf"),
    over=True
)

pdftoppm -cropbox -r 96 -png watermark-output/overlay-top.pdf watermark-output/top
pdftoppm -cropbox -r 96 -png watermark-output/underlay.pdf watermark-output/below