How to make code of converting Docx to PDF in this code?

Question

import aspose.slides as slides    
import time
from tkinter import filedialog, Tk
import os
import aspose.words as aw

root = Tk()
files = filedialog.askopenfilenames(parent = root, title = "Choose files")
files = root.tk.splitlist(files)
start = time.time()
for f in files:
    ext = os.path.splitext(f)
    if ext == ".ppt":
        pres = slides.Presentation(f)
        pres.save(f+".pdf", slides.export.SaveFormat.PDF)
    elif ext == ".docx":
        doc = aw.Document(f)     #problem part
        doc.save(f+".pdf")
end = time.time()
print("Time Taken:%f secs" %(end-start))

This is the code of converting ppt and docx to PDF.
I am trying to make the system to check whether the extension of selected files from file dialog are pptx or docx and do correct process.
But when I tried to make code of docx part, converting docx to pdf didn't work. I tried multiple times with different libraries.(docx2pdf, aspose)
Could someone help me out with this problem? Thank you