##
system("$path/pdftotext","-enc UTF-8 -nopgbrk","$path_my_pdf","$path_my_pdf.txt");
or simply
system("$path/pdftotext","-enc UTF-8","$path_my_pdf","$path_my_pdf.txt");
##
##
system("$path/pdftotext","-enc", "UTF-8","$path_my_pdf","$path_my_pdf.txt");