When it comes to counting words, in a PowerPoint presentation, several conversions have to be done. (See older post here.) Today, however, I discovered an SDL Help file which explains why counting the number of words in a .ppt/.pptx, gives you significantly different results depending on the Word Count tool you use.
This happens for 2 reasons:
1) A non-breaking space is not recognised as word separator; therefore, two words separated by a non-breaking space are counted as one word in Microsoft PowerPoint.
2) A full stop is counted as a word in Microsoft PowerPoint.
Solution proposed by SDL:
Microsoft PowerPoint has not been designed as a word processing tool and so can be incorrect in counting words. To address this issue, SDL recommends that the word count is done in another tool, for example, SDL Trados Studio or third party word counting applications.