In the process of creating a presentation, Impression FX converts (rasterizes) slides of the original document to images and compresses these images into the right format. This procedure can take a significant amount of time. In the Impression FX version for PDF, this is done once because the slides of the original PDF document cannot be edited or modified in the program. In PowerPoint, the user can edit slides anytime and information about these changes is not available to the Impression FX plugin. That is why slides are re-calculated every time you create a presentation by pressing the Create Presentation button. To avoid the time-wasting, an additional Rebuild Presentation button was added to the Impression FX interface for PowerPoint. By pressing this button, a presentation is created based on previously used slides. Use this button to create a presentation if no changes were made to the original PowerPoint document since the Create Presentation button was pressed last.