Users can import 
3DCS model files into an existing or new higher-level assembly. Additionally, 3DCS sub assemblies can be exported to individual 3DCS model files for any purpose. Imported models can be Added/Appended (create a new branch in the tree), Merged (Add new MTM's/Pt's and update existing MTM's/Pt's to the existing tree structure) or Replace (Delete all existing MTM's/Pt's and add new MTM's/Pt's to the existing tree structure)
Four different types of DCS files can be imported: WTX, WT3, W3D and GEO files.
WTX Data
This is a XML file format. The WTX file format accommodates all data saved in the model and has replaced the W3D extension. This format is the default for saving models.
WT3 Data
This is a 3DCS file which has been saved in text file format instead of binary format. The .wt3 file would be used to import a file that was viewed and modified in Microsoft Notepad or a different program.
W3D Data
A .w3d file is the standard binary file format for the MS Windows format of 3DCS. Importing a 3DCS file loads a 3DCS file into an already loaded model in the 3DCS program. It is used when smaller assemblies created separately are to be added to an existing assembly.
Notes
1. Assembly structure and component names of the loaded model is similar to imported file (corresponding parts must have the same parent.)
2. The imported file tree will be appended if similar structure cannot be found.
3. Feature points will be automatically linked to the correct surface.
User Interface / Procedure: Import / Export
The following section will outline the procedure and desired functionality for a typical modeling scenario:
Import / Export Two different Subs loaded into One Assembly
1. Bob completes RedBlue.w3d model and closes the file.
2. Joe completes GreenYellow.w3d model and closes the file.
3. Sam creates Rainbow.w3d with only the top assembly named Rainbow.
4. Sam imports RedBlue.w3d and GreenYellow.w3d.
5. Sam finds errors in Bob's and Joe's models so he has to add, modify, rename, and delete some of the points, tolerances, moves and measures in the imported sub assemblies.
6. Sam adds his own moves and measures in the Rainbow.prt and completes his model.
7. Sam exports RedBlue.w3d and GreenYellow.w3d.
8. Bob and Joe open and review the models from Sam to see what changes were made.
GEO Data
A GEO Data file is used for importing data about individual parts within 3DCS. A "*.geo" file contains parametric information about a node in an assembly. This file does not contain any information about the moves, measures or tolerances from that part. This file also does not contain the sub tree information. If a parent node in an assembly is exported as a GEO, the geometric information about only that part will be exported, not information about its children. Also, the part filename needs to have the same name as the destination part in the Tree window, to replace the point information. If the part filename is not the same, it will add the part to the end of the tree.
NOTE: For specific information look at the Creating GEO files help page.
•General Procedure:
•Open the main 3DCS model file.
•Click on File 
Import.
•Select the file type you wish to Import into your current open model file.
•Select the directory in which the file is located.
•Select the desired file to be imported.
•Click the Open button to import the file or Cancel to quit the function.
•The imported file tree will be appended to the root if a matching top level part (root) name cannot be found.
•Else the following dialog box will be displayed.
•Select Merge, Replace or Append:
Merge - All existing MTM's, GD&T, features, points, etc. will be updated with the content of the imported file. Any new 3DCS data from the imported file will be appended.
Replace - All existing parts, MTM's, GD&T, features, points, etc. will be deleted inside the matching top level assembly. All the data from the imported file will be appended.
Append - Attaches the contents of the imported model as a sub-assemblies to the existing model.