Currently Invoice module doesn't support UTF-8 export of PDF. This is not so hard to fix, if you installed correctly DOMPDF library, and enabled unicode, and also you have UTF-8 font with your special chars this is what you need to do to fix this.In invoice_helpers.inc file you have a function _invoice_get_html where there is a header of your html that is render in PDF currently it has some errors, there is twice variable "html" defined, second one without any header info so we change this and add something like
$html = '<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> <html lang="hr" xml:lang="hr" xmlns="http://www.w3.org/1999/xhtml"> <head> <meta content="text/html; charset=utf-8" http-equiv="Content-Type"> ';// $html = '<html><head>';You should change this "<html lang=" to your language.
Second part is font setting, you need to edit your template file, for example default.inc file and add your font that you have rendered for PDF use. Usually this could be made through normal CSS, but for some reason this doesn't work so i added some CSS inline in default.inc file in templates folder
echo ' <style type="text/css"> .invoice-wrapper, .invoice-wrapper td, .invoice-wrapper th, .invoice-table { color: #333333; font-family: verdana; font-size: 12px; } </style> <table class="invoice-table">....So this adds "verdana" font to my PDF output and now i have all the unicode chars i want.