Embedding a 3D model in a PDF document can add a new dimension to your interactive content. Here's how you can do it:

1. Choose the right software: To embed a 3D model in a PDF, you'll need a software that supports this feature. Adobe Acrobat Pro, for example, allows you to insert 3D models into PDF files.

2. Create or import the 3D model: You can either create a 3D model using modeling software such as Blender, Maya, or 3ds Max, or you can import an existing model in formats like .obj, .stl, or .fbx.

3. Convert the 3D model to U3D or PRC format: PDF files support 3D content in U3D (Universal 3D) or PRC (Product Representation Compact) format. Use a 3D conversion tool to convert your model to one of these formats.

4. Embed the 3D model in the PDF: Open your PDF document in Adobe Acrobat Pro and go to Tools > Rich Media > 3D. Select 'Add 3D' and then choose the U3D or PRC file of your 3D model. You can also set the initial view, lighting, and other properties for the 3D model.

5. Test and refine: After embedding the 3D model, make sure to test it in different PDF viewers to ensure that it behaves as expected. You may need to refine the positioning or size of the model to fit your document layout.

By following these steps, you can create interactive and engaging PDF documents with embedded 3D models. Whether you're showcasing product designs, architectural visualizations, or educational content, embedding 3D models can enhance the overall reading experience for your audience.