给pdf文件中添加水印,在python中主要用到两个第三方包: reportlab, PyPDF2 。其中 reportlab 主要用于生成水印模板；而 PyPDF2主要用于将水印pdf文件和需要添加水印文件进行合并操作。
安装依赖

pip install ReportLab
pip install PyPDF2

核心代码

from datetime import date
from reportlab.lib import units
from reportlab.pdfgen import canvas
from reportlab.pdfbase import pdfmetrics
from reportlab.pdfbase.ttfonts import TTFont
pdfmetrics.registerFont(TTFont('song', 'resource/simsun.ttc'))
import PyPDF2


class WaterMarkUtils:
    @staticmethod
    def create_wm_template(content,
                           width=210,
                           height=297,
                           angle=45,
                           text_stroke_color_rgb=(0, 0, 0),
                           text_fill_color_rgb=(0, 0, 0),
                           text_fill_alpha=0.3,
                           show_date=False,
                           filename='template'
                           ) -> str:
      # 生成水印模板
        file_path = f'{filename}.pdf'
        c = canvas.Canvas(f'{filename}.pdf', pagesize=(width * units.mm, height * units.mm))
        # 画布平移保证文字完整性
        c.translate(0.4 * width * units.mm, 0.4 * height * units.mm)
        c.rotate(angle)
        c.setStrokeColorRGB(*text_stroke_color_rgb)
        c.setFont('song', font_size)
        # 设置填充色
        c.setFillColorRGB(*text_fill_color_rgb)
        # 设置字体透明度
        c.setFillAlpha(text_fill_alpha)
        # 绘制字体内容
        if show_date:
            cur_date = date.today().__str__()
            content += f'({cur_date})'
        c.drawString(0, 50, content)
        c.drawString(50, 100, content)
        c.drawString(100, 150, content)
        c.drawString(150, 200, content)
        # c.drawString(200, 250, content)
        # c.drawString(250, 300, content)
        c.save()
        return file_path

    @staticmethod
    def add_watermark(content, source_path, out_path=None,angle=45, show_date=True,):
        template_path = WaterMarkUtils.create_wm_template(content, angle=angle, show_date=show_date)

        def add_wm_for_page(wm_file, page_pdf):
            # 打开水印pdf文件
            pdf_reader = PyPDF2.PdfFileReader(wm_file)
            page_pdf.mergePage(pdf_reader.getPage(0))
            return page_pdf

        source_reader = PyPDF2.PdfFileReader(source_path)
        target_writer = PyPDF2.PdfFileWriter()
        for page in range(source_reader.numPages):
            vm_pdf = add_wm_for_page(template_path, source_reader.getPage(page))
            target_writer.addPage(vm_pdf)
        if not out_path:
            target_file_name = source_path.split('.')[0] + '_wm.pdf'
        else:
            target_file_name = out_path
        target_writer.write(open(target_file_name, 'wb'))

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