We no longer use pypdf but use pypdf2, due to some bugs, we have some
pypdf objects in object database, so create a fake module so that we can
load them.

In a prefious version of this patch we have left some
Products.ERP5.NameObject in the database and saving new version of the
docuement (edit) fails with:
PicklingError: Can't pickle <class 'Products.ERP5.NameObject'>:
attribute lookup Products.ERP5.NameObject failed