merge pdf files in a given path with password. Replace your <path> and <password> to use

merge_pdf.py

import PyPDF2
from pathlib import Path

root = Path(r"<path>")
pdf_files = list(root.glob('*.pdf'))
writer = PyPDF2.PdfFileWriter()

for file in pdf_files:
    with open(file, mode='rb') as f:
        reader = PyPDF2.PdfFileReader(f)
        if reader.isEncrypted:
            reader.decrypt('<password>')
        for pageNum in range(reader.getNumPages()):
            writer.addPage(reader.getPage(pageNum))
        with open("merged_output.pdf", "wb") as out:
            writer.write(out)

Reference:
https://stackoverflow.com/questions/44375872/pypdf2-returning-blank-pdf-after-copy
https://realpython.com/pdf-python/#how-to-merge-pdfs
https://caendkoelsch.wordpress.com/2019/05/10/merging-multiple-pdfs-into-a-single-pdf/
https://www.soudegesu.com/en/post/python/open-pdf-with-pypdf2/#success-example
https://pythonhosted.org/PyPDF2/