:Pdf path/to/pdf-fileconverts, caches and opens the pdf-file.
:Unite pdf/historydisplays histories you have ever opened.
pdftotext command must have been installed in advance to convert a pdf file and
unite.vim is required to use a unite interface.
When a pdf file is edited with
:read, conversion from pdf to txt is automatically executed and open the text file instead of pdf file. You must set
g:pdf_convert_on_read to 1 to enable these features.
doc/open-pdf.txt to get more information.