...it's possibly a corrupt font, or even white set to overprint, does it view fine in indesign?
...with view > overprint preview turned on does it view fine?
...if you do a test export with a different font does it view fine in acrobat?
...to change a font globally you need to choose type > find font, then use the dialog to "change all" selected fonts to another font from the system...
...if the document exports fine with a different font then it's probably a problem font you have on your system, so try getting another copy from somewhere, or use a different typeface...
...if it still does not export to pdf correctly try opening the original file in pagemaker and do a "file > save as" to clean up the file to a fresh copy, then open in indesign...
...once opened in indesign do a file > export and choose the "indesign cs3 interchange (INX)" format from the drop down menu, then open that INX file back in indesign, ensuring all fonts needed are active, then try exporting to PDF again...
andrew