Hi. In the config file set the following and make sure that there are 755 permissions for the directories to pdftotext as well as to the pdftotext file.
PHP Code:
define('PHPDIG_INDEX_PDF',true);
define('PHPDIG_PARSE_PDF','/path/to/pdftotext');
define('PHPDIG_OPTION_PDF','');
define('PHPDIG_PDF_EXTENSION','.txt');