The first thing you need to do is determine whether the problem is with the data contained in the bar code or an issue with the scanning hardware. The scanning hardware is programmable allowing you to prefix or append printable and non-printable characters to the bar code data. Go to this link and print out the sample PDF bar code. This bar code contains the entire Gettysburg Address and is what Symbol Technologies launched as part of their marketing campaign upon their development of the PDF417 algorithm in 1990. If the bar code scans correctly, then your problem is how you are encoding the data. Check your symbology specifications such as security level and error correction code. If after scanning the sample, you get the same leading spaces, then you have a hardware issue. Try resetting the scanner or imager to factory defaults. It is difficult for me to be any more specific based on the limited information in your post. One other thing you might try is to look at what you are passing in your data stream. There are several ways to do this but one reliable way is to put your printer in dump mode and capture the escape sequence that references the PDF font. This will be different depending on whether you are printing to a laser printer using PCL or Post Script or printing to a label printer using DPL, ZPL, etc.
http://www.yourdictionary.com/images/computer/_PDF417.GIF
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