Use stdout redirection scripts for pdfinfo and, on Windows, a script to
run pdftotext hidden, which together allow for all unmodified binaries
(including, probably, symlinked system ones, though I didn't test that).
On Windows, using a .vbs does cause a brief wait cursor. The stock
pdfinfo needs the redirection script anyway, so that's unavoidable, but
on the async branch I think we'll be able to switch to pdf.js for the
page count, at which point maybe I'll try to remember how I modified the
Windows binaries to be hidden and use a modified version of pdftotext to
avoid VBScript. (We use the stock pdftotext elsewhere already.)
