The reason I suggested helping PDF them is because I have Acrobat, which means I can tweak the input settings to allow for higher quality conversion (less compression).
As far as I know, it can't be done without Acrobat; unless the scanning software may have some options for it.
Of course there are a lot of other solutions to it than using Acrobat. Conversion from any graphic format to PDF is simple, as GIMP - available on all platforms for free - does the trick. And if you need to OCR your PDF, there are also many other good offers for it. Acrobat is simple to use but has a lot of disadvantages.
Why convert to pdf if we can get them as tiff or png?
Suggest to keep it in a loss free graphical format as most people use a sort of JPG, which causes always those ugly artifacts. This is what Acrobat does internally to imported graphics. You will later on never regain the original quality of a good scan.