Staying compatible with earlier versions of PowerPoint
- People with earlier versions of PowerPoint can't open your PowerPoint 2007 (or Mac 2008) presentations.
- When you save to the earlier PowerPoint 97-2003 or similar format, your files grow very large.
Avoid using the new 2007/2010 (or in Mac, 2008/2011) effects
When you save back to earlier file formats, PowerPoint must convert any of the new glow, shadow and similar effects to images, because the earlier versions of PowerPoint don't support these effects. Images always involve more data than simple text and shapes, so your file sizes will grow.
Use the Compatibility Pack
You can leave your presentation in PowerPoint 2007 format if the people who'll view your presentation install the
Microsoft Office Compatibility Pack for Word, Excel, and PowerPoint 2007 File Formats
They'll be able to open, view, edit and save your 2007 format presentations. The special effects will still be converted to images while they're viewing the presentation, but since you'll be sending 2007 files, you won't have to send huge files.
Mac users with Office 2004 or Office X can use the Open XML File Format Converter for Mac 1.0