Preview on iPad not saving edited PDF changes across devices

There is no widely documented bug in Preview on iPad that exactly matches your description, but some users report that edits are not saving because of how iPadOS handles PDF annotations and iCloud sync.

Common causes include:

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• Markup vs. Save: On iPad, annotations are often autosaved only when you tap Done in Markup. Simply returning to the file list may not fully embed changes.
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• Flattening PDF: Unlike on iPhone, iPad might treat edits as temporary layers unless the PDF is exported or shared. Using Share → Save to Files will usually preserve edits.
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• iCloud Sync Delay: Edits may take longer to sync on iPad if the file is large or if network conditions are weak.
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• Files App Storage Location: If the PDF is stored “On My iPad” rather than in iCloud Drive, other devices will not see updates.
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A reliable workaround is to tap Done after Markup, then use Share → Save to Files to replace or create a new file in iCloud Drive. This forces the annotated version to fully save and sync.

If the problem persists, reinstalling Preview updates via iPadOS updates or restarting the iPad may help.

Reset your network settings:

1. Go to Settings > General.
2. Scroll down and tap Transfer or Reset iPad (or Reset on older iPadOS versions).
3. Tap Reset > Reset Network Settings.

You could try saving the .pdf in Notes which you would have across devices. Once saved on the devices you could delete the Note.