Update pdf2preview.py

pdf2preview.py

@@ -100,7 +100,7 @@ if st.button('Generate preview'):
         for page_num in range(num_pages):
             page = file.load_page(page_num)
             pix = page.get_pixmap(matrix = mat)
-            data = pix.tobytes("format")
+            data = pix.tobytes("png")
             img = Image.open(io.BytesIO(data))
             img_with_border = add_border(img, border=1)
             img_with_shadow = add_shadow(img_with_border, offset=(0,0), shadow=(0,0,0,255), border=20)