In Ebook Central (like EBL before it) the PDF that is generated by a print or chapter/page-download can be searched (for example, using control-f and entering a word or text string) and can also be read by a screen reader.

This is true regardless of the format the book is available in for full download (i.e., ePUB or PDF).

Note, this is in contrast to the simple image-PDFs generated by a print or chapter/page-download in ebrary.  ebrary's print and chapter/page-download PDFs are not searchable nor readable by a screen reader.