Android/iOS: Not all of the listed methods are available in these versions.
If you want to stop working on a document, you can close it at any time. If the document has been modified since it was last saved, the program automatically asks you if you want to save the document first.
To close a file, you have the following options:
In the ribbon interface
The ribbon tab File contains a Close icon 
which closes the current document.
Tip: Use the ribbon command View | Windows 
| Close all to close all currently open documents at once.
In the classic menu interface
Choose the menu command File > Close to close the current document.
Tip: Use the menu command Window > Close all to close all currently open documents at once.
In the toolbar interface (Android/iOS only)
In the group File 
, choose the command Close .
Tip: For tablets, you can close all currently open documents at once via the hamburger menu 
by choosing the menu command Window > Close all.
Tabs for documents
Above the document, you will find a bar with tabs for all currently open documents. If you click on one of these tabs with the middle mouse button, the corresponding document is closed.
Alternatively, left-click on the x icon displayed on the far right of each tab to close it.
Furthermore: If you right-click on a tab, a small menu appears with commands for closing the current document (Close tab) or all other open documents (Close all other tabs).
Via the keyboard
You can also use the shortcut key Ctrl+F4 or alternatively Ctrl+W to close the current document.
Mac: On a Mac, you have to use the key combination Cmd+F4 or Cmd+W for this purpose.