For those who are having problems with currency symbols being output as ANSI. You're most likely using version 2.3 of OS Commerce.
Here is how to fix it:
1. Download tfpdf: http://fpdf.org/en/script/script92.php
2. Unzip the file and put the tfpdf.php into your fpdf folder, eg. http://www.mystore.com/admin/fpdf/
3. Put the 'font' folder in the same location, eg. http://www.mystore.com/admin/fpdf/
4. Open up the original pdf_invoice.php file.
class PDF extends FPDF
class PDF extends tFPDF
Directly below paste:
$pdf->AddFont('Arial', '', 'arial.ttf', true);
That should be it, now open an invoice and you should see the currency symbols as they should be!
Took me about 24 hours to figure this out so hopefully it will save others some time.