The button 
New [File -> New] creates a new file. A new file can be created without any restrictions in Professional and Enterprise Versions. A new file has default properties, which can't be predefined by the user: layer's name is 0, textstyle is STANDARD, dimension style is STANDARD and other parameters. By default new files have the name NEW.dxf with an ordinal number at the end.
Before adding new elements of the drawing it is recommended to edit the values of those properties in the Properties panel which the creates elements should possess and to add new layers and styles. In the chapter Drawing Tools you can find information about the main entities which are available im ABViewer. The description of the commands editing the elements of the drawing are given in the chapterModifying Instruments.