A family of Microsoft presentation graphics products that offer tools for creating presentations and adding graphic effects like multimedia objects and special effects with text.
The most likely explanation is that your presentation uses a third-party font that is not included in the font collection present in SharePoint. You may be able to solve this by embedding the fonts. Choose File>Save As in the desktop file. In the Save As dialog, click on Tools>Save Options (to the left of the Save button). Check Embed fonts in the file, then Embed all characters. The file size will be significantly larger. Upload to SharePoint and see if the formatting looks like the file on your desktop.