Document Window
In the Text group on the INSERT tab, the "Object" button can be used to insert one document into another. By clicking on this button and selecting "Text from File," you can choose a document to embed within the current document. This allows for seamless integration of content from different files.
A text box.
A document may, or may not, contain any of the elements you mention, including tables.
It is to Edit
yes it can
In this case it is a hidden text. Hidden text displays in the electronic form of the document but will not be printed out.
monitor
To insert a portion of text at the top of the document, you have double click on the top and then a section called header will come up. Then you type the text in that section. This text will come at the top of every page you work on after.
The insert menu is for inserting various things like shapes, tables, pictures, charts, headers, footers text boxes etc into a document. Click on the insert menu and have a look. Try to insert a table it is not hard to do.
Footer
Word art
Click Insert tab to expand, look for Object and click it to show you 2 options, choose Text from File.. and navigate to document you want to insert.