In PDF Annotator, you can keep multiple documents open at the same time, edit and switch between them.
For each open document, PDF Annotator will display a tab right below the main toolbar, showing the document's file name. Click on a tab to switch to that document. Click on the Close icon right to the file name to close the document. The tab order can be rearranged by repositioning the tabs with the mouse.
Under Extras Settings Display Document Tabs, you can decide if you prefer to display the bar containing the document tabs always, as soon as one document has been opened, when at least two documents are open, or never. For very long document titles, the title will be shortened depending on the Tab width setting.
By default, when you close PDF Annotator, and open it again, PDF Annotator will come up with no open documents. If you prefer to reopen all documents and tabs as you left them before closing PDF Annotator, enable Restore document tabs from last session under Extras Settings Display Document Tabs.