If you're into 3D modeling and printing, you've probably come across OBJ files. Opening OBJ files is essential for working with 3D models created in software such as Blender, Maya, or 3ds Max. Here's how to do it:

1. Use 3D Modeling Software: To open an OBJ file, you'll need 3D modeling software such as Blender, Maya, or 3ds Max. These programs allow you to import and manipulate 3D models in various file formats, including OBJ.

2. Import OBJ File: Once you have the 3D modeling software installed, you can import the OBJ file by going to the 'File' menu and selecting 'Import.' Choose the OBJ file from your computer and click 'Open.' The software will then import the OBJ file into the 3D workspace.

3. Manipulate the 3D Model: After importing the OBJ file, you can manipulate the 3D model as needed. This may include scaling, rotating, or adding textures to the model.

4. Export or Print: Once you've made the necessary changes to the 3D model, you can export it to various file formats for 3D printing or use it within other software for further editing.

Additionally, there are online OBJ file viewers available that allow you to open and view OBJ files without the need for 3D modeling software. These online viewers provide a quick and easy way to visualize OBJ files without any installation.

Remember to ensure that you're using reputable sources to download and open OBJ files, as there can be security risks with certain file downloads. Always have antivirus software installed and updated on your computer to minimize any potential threats.

In conclusion, opening OBJ files is a fundamental skill for anyone involved in 3D modeling and printing. By using the right software and following these simple steps, you can easily open, edit, and manipulate OBJ files to bring your 3D design ideas to life.