Opening a 3DM file can be done with the right software. A 3DM file is a file format used by Rhinoceros, a 3D modeling software. Here's how you can open a 3DM file:

1. Using Rhinoceros: If you have Rhinoceros installed on your computer, simply double-click on the 3DM file, and it should open automatically in the software.

2. Using Other 3D Modeling Software: Some other 3D modeling software can also open 3DM files, such as Autodesk Fusion 360 or SolidWorks. You can try importing the 3DM file into these applications to view and edit it.

3. Using 3DM Viewer: If you don't have any 3D modeling software installed, you can use a 3DM file viewer to open and view the contents of the file. There are several 3DM file viewers available for free online, which can be downloaded and used to open 3DM files without the need for additional software.

4. Online Conversion: If you still cannot open a 3DM file, you can try online file conversion services that can convert 3DM files to more common file formats, such as STL or OBJ, which can then be opened using a wider range of software.

Remember, 3DM files are generally used for 3D modeling and design, so you may need specialized software to open and work with them effectively. Make sure to use reputable software and tools when dealing with 3DM files to avoid any potential security risks.

By following these simple steps, you can easily open and view 3DM files on your computer, even if you don't have the specific modeling software installed. Whether you're a 3D design professional or someone who needs to view a 3DM file for a specific project, these methods will help you access the content of 3DM files with ease.