pip install pypdf2 The code: import PyPDF2 pdfFile = open('example.pdf', 'rb') pdfReader = PyPDF2.PdfFileReader(pdfFile) pdfWriter = PyPDF2.PdfFileWriter() for pageNum in range(pdfReader.numPages): pdfWriter.addPage(pdfReader.getPage(pageNum)) pdfWriter.encrypt('password') resultPdf = open('encrypted_output.pdf', 'wb') pdfWriter.write(resultPdf) resultPdf.close()