Final answer:
When exporting an outline from Word to PowerPoint, the new file will have a .pptx extension, which is the default extension for PowerPoint presentations.
Step-by-step explanation:
When you export an outline from Microsoft Word into Microsoft PowerPoint, the new file will have a .pptx extension. This is the default file extension for PowerPoint presentations, signifying that it is a PowerPoint Presentation file. Files with a .docx extension are Word documents, while .pub is the file extension for Publisher files, and .xlsx is used for Excel spreadsheets. Therefore, it's important to remember that when you're exporting content from Word to be used in PowerPoint, you're creating a presentation file.