While I can search content via Windows Search on most PDFs, I occasionally come across PDF files with contents that are not searchable; even though they contain regular, selectable/copyable text with no format abnormalities.
An example is the PDF of this article: http://www.ncbi.nlm.nih.gov/pubmed/23870130 (both the CellPress version and the PMC version have unsearchable contents)
Is there a way to make all such PDFs searchable? Or does one have to use specific solutions for each document? What would these solutions be?