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CC3 allows you to open more than one file at a time. This is feature of the CAD engine, and is not implemented as a main stream CC3 feature. Use it with caution.
Additional drawing files can be opened in two ways:
As separate drawings
Files opened in this manner are independent of each other. For instance, a single line cannot be drawn from one drawing to another, nor can an entity be dragged from one drawing to another. The clipboard must be used to directly transfer entities between separate drawings.
As overlay (or reference) drawings
After a file has been loaded using the normal OPEN command, overlays or reference drawings can be loaded atop it. Overlays are completely separate drawings, and always maintain their separate nature. When an overlay is opened atop a separate file, it never integrates itself with another drawing. Rather, it shares the same coordinate space. Overlay drawings can be opened and edited independently. A reference file is simply an overlay that is read-only. A read-only file is one that cannot be edited.
Note that overlay/reference drawings can only be loaded on the drawing loaded with the OPEN or NEW command. Successive drawings loaded with the SEPARATE FILE command cannot possess overlays for this session.
To understand overlays better, it may help to compare them with parts, their most similar traditional CC3 feature. Both overlays and parts are maintained as separate regular drawing files. But parts differ from overlays in the following key aspects:
· Once a part is inserted into a target drawing, it becomes fully integrated into the target drawing. Every time the target drawing is loaded in the future, the parts contained therein also load. Overlays, on the other hand, remain conspicuously discrete. Overlays must be singly loaded every time the primary file is newly loaded. Overlays never auto-load, and they share no natural association with any other file.
· Since an inserted part’s elements are integrated into the target drawing, subsequent editing of the inserted part does not affect the original part file in any way. Overlays, however, are the source file. If you edit an overlay while it is loaded, and then save it, the overlay file is modified to reflect those changes.
· Conversely, subsequent editing of the source part file will not affect parts that have already been inserted. There is no dynamic association between the source part file and inserted parts. Overlays are always displayed in their current state.
As you can see, parts and overlays share some similar qualities. They are both separate drawing files that can be "combined" with others. But, functionally, they are completely different.
Parts, as their name suggests, are used to make drawing entities portable for use in other drawings.
Overlays serve more of an administrative purpose. Use overlays to logically separate an otherwise large drawing into smaller, more manageable drawing tasks. An example might be that of a facility engineer who controls the master plant layouts, but allows sectional overlays to be modified by personnel relevant only to those areas. Or perhaps a single drawing is so large that it affects your computer system’s performance. Separating the drawing into smaller, more efficient overlays will facilitate editing, while allowing all elements to be easily recombined when needed.
Only one overlay system can be loaded in CC3 at one time.
When you select Multiple Drawings, a sub-menu appears with five different multiple file commands.