When copying text from a PDF, we often get the text line by line.
https://github.com/aoloe/scribus-script-repository/tree/master/join-lines
Today, I wrote a script that joins those lines in paragraphs.
If you copy the "scribus-script-repository" repository on your disk and add it to your script folders in "Preferences > Scripts", then you can simply run it from the Scripts menu:
join-lines.gif
Of course, you can also just copy the Python file in your own collection of scripts.
Please read the README in the folder linked above for the exact behavior of the script.