Use pdf2htmlEx to convert PDF to HTML

The library we use is found under https://github.com/coolwanglu/pdf2htmlEX

Integrate the process, so the uploaded PDF is converted and the converted files (including images) are moved to the correct place, where the iframe loads them.

Use the call

pdf2htmlEX --embed-image 0 --hdpi 72 --no-drm 1  --decompose-ligature 1 <filename>.pdf 

The parameters are the correct once to use.

I case of multiple PDFs uploaded for the task, the PDFs should be merged into one PDF before converting to an html-file. An easy way to do this is to use Ghostscript. the following example shows how to merge 2 PDFs (org_1.pdf and org_2.pdf) into one new file merged.pdf:

gs -dBATCH -dNOPAUSE -q -sDEVICE=pdfwrite -dPDFSETTINGS=/prepress -sOutputFile=merged.pdf org_1.pdf org_2.pdf