You have to export project and activities separately (in csv format) and import them, project first, activities last.
If their is no ambiguity on project name, his will work with default export.
Otherwise you'll have to export ids (and not names) and after import of project retreive project id and replace exported value with this one in idProject of activity file.

So it seems not possible to export a project and all its objects : activities, jalons, decisions, questions, etc. in a pdf format or xls one ?
It could be a great thing to create this fonction, if not 🙂
All the best et bonne année
Christophe

No,
It look like similar post requesting for project dashbord : everyone would like to customize to its own need.
So maybe we'll develop this as a plugin.

But if it is a plugin, it won't be free?
Christophe

No.
Everything can't be free, otherwise Project would quickly die....
Everybody's work must be rewarded, one way or another.

Yes, i understand... but the possibility to export all the object of a project seems to be a very important and useful tool...
Christophe