Originally Posted by owl123
Actually you might try changing PDF's font with... a hex editor. The font can't differ much though or the text will look all messed up.
Yeah, the kerning (i.e. positioning) of each character is done according to the font used when the PDF was created. New font characters get placed in exactly the same positions, even if they are shaped differently. I remember trying to read PDF files created by Acrobat on an open-source reader called xpdf about 10 years ago, and the text looked horrible because the Adobe fonts weren't freely available back then. When Adobe released their fonts, the rendering in xpdf improved dramatically for those files.
As fjtorres mentioned, creating a new PDF file is best so that the words are kerned using the new font.