Interactive PDFs are of course a well established digital resource and many visitors will already have PDF reader apps installed on their phones. (iBooks for example is now provided on IOS devices as standard).
The feature of the smartphone guide is the way it designs the PDF file so as to mimic app functionality. It also takes advantage of the fact that it can use either vector or raster maps. This allows it to offer zoom in functionality of up to 16X in line with the capabilities of the PDF reader app (some are better than others).