为pdf文件添加水印，要求： 1，可以文字水印，也可以上传图片作为水印 2，可以调节水印大小(0到100)，透明度(0到100)，旋转角度，翻转(无，水平翻转，垂直翻转)，和选择水印位置(九宫格或平铺) 3，使用python语言并显示完整代码 4，使用PyPDF4

模块

以下是实现以上要求的Python代码：

from PyPDF4 import PdfFileWriter, PdfFileReader
from reportlab.pdfgen import canvas
from reportlab.lib.units import mm
from PIL import Image
import io

def add_watermark(input_pdf, output_pdf, watermark_text=None, watermark_image=None, size=50, opacity=50, angle=0, flip=None, position='center'):
    # Open the input PDF file
    input_file = open(input_pdf, 'rb')
    pdf_reader = PdfFileReader(input_file)

    # Create a new PDF writer
    pdf_writer = PdfFileWriter()

    # If watermark text is provided, create a watermark PDF
    if watermark_text:
        # Create a canvas to draw the watermark text
        watermark_canvas = canvas.Canvas('watermark.pdf')

        # Set the font and font size for the watermark text
        watermark_canvas.setFont('Helvetica', size)

        # Draw the watermark text in the center of the canvas
        watermark_canvas.drawCentredString(105*mm, 148*mm, watermark_text)

        # Save the watermark PDF
        watermark_canvas.save()

        # Open the watermark PDF file
        watermark_file = open('watermark.pdf', 'rb')
        watermark_reader = PdfFileReader(watermark_file)

        # Get the first page of the input PDF file
        input_page = pdf_reader.getPage(0)

        # Get the first page of the watermark PDF file
        watermark_page = watermark_reader.getPage(0)

        # Merge the pages
        input_page.mergePage(watermark_page)

        # Add the merged page to the output PDF writer
        pdf_writer.addPage(input_page)

        # Close the watermark PDF file
        watermark_file.close()

    # If watermark image is provided, create a watermark PDF
    if watermark_image:
        # Open the watermark image file
        with Image.open(watermark_image) as img:
            # Create a buffer to hold the PDF data
            img_buffer = io.BytesIO()

            # Convert the image to PDF and save it to the buffer
            img.save(img_buffer, 'PDF', resolution=100.0)

            # Set the buffer position to the beginning
            img_buffer.seek(0)

            # Open the PDF data as a reader
            watermark_reader = PdfFileReader(img_buffer)

            # Get the first page of the input PDF file
            input_page = pdf_reader.getPage(0)

            # Get the first page of the watermark PDF file
            watermark_page = watermark_reader.getPage(0)

            # Merge the pages
            input_page.mergePage(watermark_page)

            # Add the merged page to the output PDF writer
            pdf_writer.addPage(input_page)

    # If neither watermark text nor watermark image is provided, simply copy the input PDF file to the output PDF file
    if not watermark_text and not watermark_image:
        for page in pdf_reader.pages:
            pdf_writer.addPage(page)

    # Set the opacity of the watermark
    opacity_percent = opacity / 100.0
    pdf_writer.encrypt(user_pwd=None, owner_pwd=None, use_128bit=True)
    pdf_writer._encrypt_metadata=False

    # Get the output PDF file object
    output_file = open(output_pdf, 'wb')

    # Set the watermark position
    if position == 'center':
        x = 0.5
        y = 0.5
    elif position == 'top_left':
        x = 0.1
        y = 0.9
    elif position == 'top_center':
        x = 0.5
        y = 0.9
    elif position == 'top_right':
        x = 0.9
        y = 0.9
    elif position == 'center_left':
        x = 0.1
        y = 0.5
    elif position == 'center_right':
        x = 0.9
        y = 0.5
    elif position == 'bottom_left':
        x = 0.1
        y = 0.1
    elif position == 'bottom_center':
        x = 0.5
        y = 0.1
    elif position == 'bottom_right':
        x = 0.9
        y = 0.1

    # Loop through all pages of the output PDF writer
    for page in pdf_writer.pages:
        # Get the page width and height
        width = page.mediaBox.getWidth()
        height = page.mediaBox.getHeight()

        # Create a new content stream for the watermark
        watermark_content = PdfFileWriter().addBlankPage(width, height)

        # Set the opacity of the watermark
        watermark_content.getPage(0).gfx.setAlpha(opacity_percent)

        # Rotate the watermark
        if angle != 0:
            watermark_content.getPage(0).rotateClockwise(angle)

        # Flip the watermark
        if flip == 'horizontal':
            watermark_content.getPage(0).scale(-1, 1)
            watermark_content.getPage(0).translate(-width, 0)
        elif flip == 'vertical':
            watermark_content.getPage(0).scale(1, -1)
            watermark_content.getPage(0).translate(0, -height)

        # Draw the watermark on the content stream
        if watermark_text:
            watermark_content.mergePage(watermark_reader.getPage(0))
        elif watermark_image:
            watermark_content.mergePage(watermark_reader.getPage(0))

        # Add the content stream to the output page
        page.mergePage(watermark_content.getPage(0))

        # Set the position of the watermark on the output page
        page.mergeTranslatedPage(watermark_content.getPage(0), x*width, y*height)

        # Add the modified page to the output PDF file
        output_page = page
        pdf_writer.addPage(output_page)

    # Write the output PDF file
    pdf_writer.write(output_file)

    # Close the input and output PDF files
    input_file.close()
    output_file.close()

# Example usage
add_watermark('input.pdf', 'output.pdf', watermark_text='CONFIDENTIAL', size=50, opacity=50, angle=45, flip='horizontal', position='center')
add_watermark('input.pdf', 'output.pdf', watermark_image='watermark.png', size=50, opacity=50, angle=45, flip='horizontal', position='center')