问题 I have two pdf files of the same length, let's say pdf1.pdf and pdf2.pdf. I'm trying to watermark each page of pdf1.pdf with pdf2.pdf (i.e., page 1 of pdf1.pdf with page 1 of pdf2.pdf, page 2 of pdf1.pdf with page 2 of pdf2.pdf ...). However, I'm really struggling with how to loop them around (I'm new to programming). For example, I tried this: import PyPDF2 from PyPDF2 import PdfFileMerger from PyPDF2 import PdfFileReader, PdfFileWriter output = PdfFileWriter() ipdf = PdfFileReader(open(