Stories stay in order across pages
Newsletters use linked text boxes: one story runs from page 1 into page 3. The open-source parser inside LibreOffice and PubHarbor has never implemented that link, so it pastes the whole story on every page and leaves the last one blank; that bug has been open since 2013, and PUB Reader's reviews describe the same symptom. PubFile follows the links, so page 2 starts where page 1 ended.
See it on the file from the bug report
Files you can keep editing
PubFile writes IDML, the exchange format that Affinity (free), Affinity Publisher 2 and Adobe InDesign open. Text stays text, boxes stay boxes, pictures come along in a folder.
Nothing leaves your Mac
No upload, no account, works offline. Parish directories and class lists stay where they are. Originals are read, never rewritten.
A report that tells you what to check
For every file: which fonts were substituted, how much of each story was placed on each page and what did not fit, and which objects could not be converted. It says what broke instead of reporting zero warnings on a blank page.