from pikepdf import Pdf, Name

inputpdf=r"u:\Dropbox\!!!Days\Downloads Z230\Dokumentace\a.pdf"

# # Open the PDF file
# with Pdf.open(inputpdf) as pdf:
#     # Ensure the PDF has a Catalog dictionary
#     if '/Catalog' not in pdf.Root:
#         pdf.Root['/Catalog'] = {}
#
#     # Set the OpenAction to fit the page
#     pdf.Root['/Catalog']['/OpenAction'] = [pdf.pages[0], Name.Fit]
#
#     # Save the modified PDF
#     pdf.save('output.pdf')

from pikepdf import Pdf, Dictionary, Name

pdf = Pdf.open(inputpdf)
pdf.Root.PageLayout = Name('/SinglePage')
pdf.Root.PageMode = Name('/UseNone')
pdf.save('output.pdf')