Default font (used by PDF library) doesn't support all UTF8 symbols.
So if you use Chinese,Arabic,Cyrillic,Hebrew  -- you must install new font.

Please, use this way.

1. dowload zip from

2. run ftp client and create folder "fonts" inside active theme

3. upload file Code200365k.ttf to folder "fonts".

4. add following PHP code to functions.php

    $fpdf->setFontPath( dirname( __FILE__ ) ."/fonts/"); 
    $fpdf->AddFont( 'Code200365k', "", "Code200365k.ttf" );
    $fpdf->AddFont( 'Code200365k', "B", "Code200365k.ttf" );
    $fpdf->SetFont( 'Code200365k', '', 12 );
    return $fpdf;