When you are working online, you can delete a document ONLY when it is new and not under version control or when it is checked in to the server. You cannot delete a document that is under version control but checked out to you. If you try to delete a version-controlled document that is checked out to you, you receive the message "Not all of the documents you selected were processed". If you click the View activity log link, you also see the comment "Document must be checked in to delete".
A document is deemed "under version control" after the first check-in to the server. From that point on, the Developer keeps track of changes that are made by various authors and automatically assigns a version number. This is important since a deleted a document that is under version control is restorable, unless purged by your administrator. You can also roll back to earlier versions of a document that are under version control using the History command on the Document menu. It is important to note that new documents not under version control can be deleted but CANNOT BE RESTORED.
Note: You cannot delete versioned documents when the Developer is offline.
View Deleted Documents in the Library
Version-controlled documents that are deleted can be displayed and restored from the Deleted documents view in the Library.
View Deleted Documents and the Outline Editor
When you delete a document from the Library it is immediately removed from the folder in which it lives. However, the appearance of a deleted document in the Outline Editor is not as immediate. For example, if you delete a version-controlled module, section, or topic from the Library, the document name continues to appear in the hierarchy of any outline in which it is used, but now appears with an "X" on top of the document icon.
When you select a deleted document from the Outline Editor, you may see a message in either the Concept or Introduction pane that a linked document is deleted. For example, this message appears if you select a section with a linked web page (as the Concept) that has been deleted. To correct this situation, you should restore the deleted document or remove the link.
Non version-controlled documents that are deleted from the Library display the 
Missing Document link in the Outline Editor. Since these documents are not restorable, your only option is to remove the document from the outline using the Delete Link command on the Edit menu.