You could export your PowerPoint presentations to Word, then create a new Word document and copy/paste all the required content from the other documents into it. The same could be done via Insert|Object>Text from file. Alternatively, you could use INCLUDETEXT fields (via Insert|Object>Text from file, with the 'insert as link' option) to link the new file to the source documents, so that updates to the source files would be reflected in the consolidated one.

Any other process that turns each individual file into PDFs will result in a plethora of PDFs that you would have to use other software to combine.

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]