Any set of PDFs can be used as a starting point regardless of their age, the application that made them (e.g. QuarkXPress, iBooks Author or unknown) and there is no restriction on the fonts that have been used or colour mode (e.g. CMYK graphics).
Only the trim size of the PDF page is used. Any bleed areas and trim marks will be cropped off on import meaning existing print PDFs can be quickly re-purposed as eBooks.
Most PDFs contain selectable text and when they do this text carries through to become searchable in the resulting ebook. PDFs without text may first be passed through a optical character recognition (OCR) tool like Adobe Acrobat.
Either a single PDF containing multiple pages or multiple PDFs can be used and if working with a ‘black plate change’ workflow it is possible to overlay text PDFs over base artwork PDFs on the same page.
Spread PDFs can be used and split back out into facing pages or alternatively, for landscape documents, a single page to view can be used.
PDFs are placed onto a newly created ‘FLO_PDF’ layer which can be mixed more InDesign content and other CircularFLO layers containing hyperlinks, animations etc. with your PDF artworks as required.