Yes, projects made with the previous version WebSite X5 Evolution 9 can be opened and updated in WebSite X5 Evolution 10.

Converting a project is simple:
In WebSite X5 Evolution 9, open the project you want to update, go to Step 5 and choose Export the Project, indicating the destination folder. The result will be a compressed .IWZIP file that contains both the project file and linked files.

In WebSite X5 Evolution 10, in the Project Selection window, click on the Import button and select the .IWZIP file of the previously exported project. Your old project will now appear in the list of existing projects (for the new version).
Select the imported project from the list and click on Next to make the necessary changes.

Import times vary according to the size of the project and the number of files linked to it: the .IWZIP file must be expanded and the library and preview files have to be created.

However, these operations only have to be done once: after the first time, the document will open faster.

Further informations are available in the document “ Converting project”: http://static.incomedia.eu/websitex5.com/v10/v9tov10_conversion_en.pdf