I used Trados 2011 Freelance to create a project around the PDF file to be translated, and simply saved that project, not knowing that the editor was going to be using Trados 2009, and not realizing that this might cause a problem later on.
[Edited at 2013-09-09 18:48 GMT]
You have not used Packages. This is just am sdlxliff file and you can share these between versions. The editor can make changes and send it back.
The oonly problems are if the editor wants to print preview or to save the target then they may not be able to if the filetypes between the versions are different. This is where packages come into play and avoid these issues.