What’s the Difference Between Multiple Open Documents, Multiple Inventor Instances, and Running Inventor on Two Separate Computers?

by Vladimir Michl

When you need to work on two unrelated CAD projects at the same time — whether in Inventor, AutoCAD, Revit, Civil 3D, Plant 3D, Electrical, Max, Fusion, or similar tools — you can approach it in several ways. Each method behaves differently in terms of performance, licensing, and risk of conflicts.

1) Multiple Documents in a Single Application Session (MDE)

Many CAD applications support MDE — Multi‑Document Environment, which allows you to open several files within one running instance of the software.

Why this is the preferred method:

• The application manages file access and internal conflicts automatically
• Memory consumption stays low
• Only one license is used
• Switching between projects is fast and safe

Some programs require you to close the current project before opening another, but when MDE is available, it is the most stable and recommended option and workflow.

2) Running Two Separate Instances of the Same CAD Application

Another option is to start two independent copies of the CAD program and load a different project into each one.

While possible, this approach has drawbacks:

• Some applications (e.g., Fusion) actively try to prevent multiple instances
• Parallel sessions may write to shared configuration files or the Windows registry, causing settings conflicts
• Software that relies on databases or linked files (Electrical, Plant 3D, Inventor, Fusion) is especially prone to issues
• RAM usage doubles
• Clipboard sharing works, but…
• Only one license is consumed if both instances run on the same PC

Because of the risk of corrupting settings or shared data, this method is not recommended.

3) Running the Application on Two Different Computers (or Virtual Machines)

The third scenario is using two separate machines, each running its own installation of the CAD software.

Characteristics of this setup:

• Both environments are obviously completely isolated
• Clipboard cannot be shared
• Hardware requirements double
• You need two licenses
• Using the same user account on two machines with only one license may violate licensing terms of your CAD software