Go to view “All documents'” and type CTRL+T
It il will select all your documents and display count in the message bar, in the bottom of your screen.
Don’t forget to deselect all (in the Edit menu) after !
Another way is to open the properties pane (File/Application/Properties on the menu) for the database and choose the second tab (marked with a lowercase i). This will show you the size of the database and the number of records.