1. Download a free extension file from the Microsoft official website. The web link is:
http://www.microsoft.com/downloads/details.aspx?FamilyID=4d951911-3e7e-4ae6-b059-a2e79ed87041&displaylang=en
2. Execute the downloaded file, named as “SaveAsPDFandXPS.exe”, and the extension will be installed.
3. Open PowerPoint 2007. Click the big Microsoft Office button on the left-most top. Move the cursor upon the "Save As" button and it will show a sub-menu. Then, click the “PDF or XPS” button in the sub-menu.
4. Choose a file name to save it as a PDF file.
This method will generate a PDF file whose quality is closer to the original PowerPoint slides than any other software does (e.g., Adobe Acrobat, etc.). Generally it can prevent the fonts from being distorted and ameliorate losses of image quality during the conversion to the PDF file. However, it has one drawback. If one uses the Adobe Acrobat Reader in Linux to read the PDF file generated by this method, one would find the font looks different from the original file. This problem only occurs if one uses the Linux version of Acrobat Reader. If one uses other PDF readers in Linux to display it, there won't be any problem. Except for the Acrobat Reader in Linux, Acrobat Reader in Windows or Mac OS can both display this PDF file normally.