If the headline was a bit confusing, this is what I mean:
I copied text from one Scrivener project and pasted it into another (Scrivener project).
In the original the text filled the whole writing column / writing area. But once it was pasted into the new project, it turned into a much narrower “column”, only filling half of the width of the writing area. And I don’t know how to spread the text to fill the whole writing area in the new project.
It sounds like the same problem posted here. Note that was in the Mac section, but the issue and solution is the same. The Ruler command is Ctrl-Shift-R.
Another point worth mentioning in your case (that I would not have recommended to the other user, who had complex formatting in their document) is to just clean up formatting after paste. You will find very often that formatting doesn’t always work the way you want when pasting between browsers, word processors, and even documents within the same programs. The Documents/Convert/Formatting to Default Text Style command is designed for just this problem.
