Fix 'ModuleNotFoundError: No module named 'pypdf'' when running samp…

[th3coop]

Was taking this module for a trial run and found the sample code wasn't working. PR to resolve the error.

Repro:

• run the recommend command from the repo root
  python3 ./samplecode/basic_features.py
• get the following error:

 > python  .\samplecode\basic_features.py
Traceback (most recent call last):
  File ".\samplecode\basic_features.py", line 11, in <module>
    from pypdf.pdf import PdfFileReader, PdfFileWriter
ModuleNotFoundError: No module named 'pypdf'

[NotWearingPants]

Why not also fix the other 2 samples? (PDFComments2XL.py & MergingComments.py)

They both just have import pypdf as PDF instead of import PyPDF4 as PDF

[th3coop]

Added those files.

[th3coop]

Thanks for the review @NotWearingPants.