Which file type is NOT supported for upload via the image widget?

The correct answer indicates that PDF files are not supported for upload via the image widget in Smartsheet. The image widget is specifically designed to display images, and common image file types such as JPEG, PNG, and GIF are supported due to their compatibility with image rendering and display. By contrast, PDF files are structured differently; they are document files that may contain text, images, and other types of content but are not categorized as images themselves. Therefore, the functionality of the image widget is limited to formats that portray visual content directly, which excludes PDFs. This distinction is essential for users to understand the capabilities and limitations of the image widget when working within Smartsheet for designing dashboards or presenting visual data.