When the PDF image format was first made available for DPS articles, the format was limited. Most importantly, interactive overlays were not supported in PDF-based articles, so most designers stuck with the JPG/PNG image format unless they wanted users to be able to pinch & zoom on a page.
With the v18 release of the tools, that changed. Now, all interactive overlays in PDF articles work just as well as they do in JPG/PNG articles.
With the new retina display iPad, using the PDF format has now become the recommended choice for image format. PDF articles are smaller than JPG/PNG articles, and vector content is maintained, resulting in improved scaling. However, there are still some differences between the PDF and JPG/PNG image formats that you should be aware of.
Advantages of PDF
PDF articles are usually much smaller than JPG/PNG articles, especially long articles.
Pages in PDF articles can have pinch and zoom enabled.
All interactive overlays are now supported in PDF.
The combination of small file size and vector text makes PDF the ideal format for the new retina display iPad.
Disadvantages of PDF
Only iOS viewers support the PDF image format. You cannot preview PDF articles in the Desktop Viewer or in Android devices.
Smooth Scrolling articles cannot use the PDF image format. If you import multiple articles into a folio in which the default image setting is PDF, the Smooth Scrolling articles are converted to JPG or PNG.
There is sometimes a brief load time when flipping to a PDF article.
In the Folio Producer Editor, preview thumbnails are not available for PDF articles. This shouldn’t be a problem as long as you’re aware of this limitation, but some people look at their PDF folios in the Folio Producer Editor and think their content is missing.