Open command (File menu)
Use this command to open an existing document in a new window.

EditPlus displays the File Open dialog box so you can choose documents to edit. You can open multiple documents at once. Use the Window menu or Document Selector to switch among the multiple open documents. See Window 1, 2, ... command and Document Selector.

You can create new documents with the New command.

Shortcuts
Toolbar:    
Keys:    Ctrl+O