From Scribus Wiki

What’s New in Scribus 1.5.0?

This is a cursory overview over the most important changes in Scribus compared to the latest stable version 1.4.x.

Please note that the file format has changed and is not backwardly compatible with any prior stable version (1.4.x or earlier). To be precise, you will not be able to open 1.5.x files with version 1.4.x or any earlier version.

Also note that the 1.5.x series is not an officially stable version. Instead, all 1.5.x versions are technical previews of the upcoming stable Scribus 1.6.0! If you try to do some serious work with 1.5.x, you do so at your own peril.

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