When content is loading, show an activity spinner or a progress bar so users know something is loading and gauge how long it will take to load.
When loading content, but you’re unsure how long it will take or you can’t measure the size of the download, use an activity spinner at the minimum.
Progress bars show a horizontal indicator displaying the percentage completed, and give a visual cue about how long a task is expected to take.
If there are multiple files or tasks processing simultaneously, a progress circle indicator may be more appropriate for lists or table layouts.
When tasks are complete, display a checkmark inside the circle.
When file processing is complete, replace it with the file format icon.