from  PyPDF2 import  PdfFileReader,PdfFileWriter

写pdf=PdfFileWriter()
for  i in range(1,5):
    读pdf=PdfFileReader('{}.pdf'.format(i))
    for  j  in range(读pdf.getNumPages()):
        写pdf.addPage(读pdf.getPage(j))

with  open('合并后的pdf文件.pdf','wb')  as  f:
    写pdf.write(f)