Merge vs. Link vs. Open

The possible ways of using the model data, CAD drawings and reports received from another application in ARCHICAD are the following:
Merge
Use Merge to add the model or drawing content (or part of it) to the currently running ARCHICAD project. Merged model data are converted into native ARCHICAD elements, which can then be used as a protected or editable reference. The imported content, used as a reference, is separated from the host project elements, and can be displayed together or independently from the original project data by choosing a visualization technique.
See Visualization of Imported Content.
Merged IFC data are converted to native ARCHICAD properties, so they can be searched, listed, and used in the model.
The Detect IFC Model Changes command applies the merging algorithm for the detected geometrical differences between two (old and new) states of received models (two IFC files exported from the same application).
See details at Change Detection.
Note: Before merging a file, you should save the running ARCHICAD file.
For details on ARCHICAD’s Merge function, see Merging Files to ARCHICAD.
Link
As another “reference” possibility, you may open a received 3D model as a new ARCHICAD project first - e.g. to visually filter out the parts you will need - then link the project, or a part of it, to your current project as a Hotlinked Module, which will serve as (non-editable) content.
See also Hotlinked Modules.
Note: You cannot directly hotlink an IFC file to ARCHICAD. However, when you open an IFC project and hotlink its elements to another ARCHICAD project, all IFC parameters are retained, including the elements’ classification by structural function and position, as well as the elements’ profile, material and other IFC properties such as Fire rating. IFC data in linked modules are also treated as native ARCHICAD properties, so they can be searched and listed in the host project.
CAD drawings and reports (PDF) can be directly linked to the current ARCHICAD project. Depending on the file formats, use XREF and/or Drawing connection.
See XREFs and Importing PDF Files As Drawings.
Open
The Open command launches a model or CAD drawing as a separate ARCHICAD file, independent of any other project currently open in ARCHICAD. This imported file can be added later as a reference to the appropriate part of another ARCHICAD project as mentioned before.
The following figures summarize the import possibilities by the type of the received data: