Trash contains all the documents that you have deleted in 'History','Folders' and 'Books'.

Click on the Trash tab to view your documents ordered by their date and time of deletion.Documents are grouped by date (Today, Yesterday, .., Last week).
Deleted documents can be restored into the History, Folders andBooks abs by clicking on Restore in the File Menu or by clicking on Restorein the contextual menu.
Deleting documents from trash is final and also deletes any actions linked to these documents.