Documents accessed via "Show earlier versions" cannot be edited and saved back to the server and will be opened read-only.
CtrlPrint saves each successive version of a document that is saved to the server. This includes a PDF for each version, and any additional PDF presets which have been added to the project.
To access an earlier version of a chapter select first the company, then the project, and then the chapter from the left menu. From the "Chapter" menu select "Show earlier versions":
You will then see a list of every version of the chapter that has been saved to the server:
You can see when each version was created and by which user. Links are provided for downloading a PDF, a read-only file for opening in InCopy/InDesign (the "Get document" option), view comments and access additional PDFs.