Search result of some pdf files returns weird code instead of & sign and other special characters. I first thought this had to do with a missing parameter for the helper program. I re-indexed with the following corrected helper config:

/usr/bin/env pdftotext -enc UTF-8 %file% -

This did not solve the problem however. When I run this on the command line of the server specifically on the problematic PDF file, then it returns the correct UTF-8 characters, but I see still these codes in Drupal's search result.

I will try to produce a test PDF file and attach it here with quotes of result tomorrow.