PDF417 is a two-dimensional, stacked, public-domain barcode developed in 1990 by Symbol Technology. (PDF stands for “Portable Data File.” )
It is a multi-row, continuous, variable length symbology that has high data capacity of storing up to about 1,800 printable ASCII characters or 1,100 binary character per symbol. The symbol is rectangular; the shape of the symbol can be adjusted to some extent by setting the width and allowing the height to grow with the data. It is also possible to break large amounts of data into several PDF417 symbols that can logically linked.

Each symbol has between 3 and 90 rows. Each row contains a start pattern, a left row indicator, from 1 to 30 data characters, a right row indicator, and a stop pattern. Both the number of rows and their length are selectable, allowing the aspect ratio to be adjusted to particular labeling applications. There are no separator bars between rows.

Each symbol character consists of 4 bars and 4 spaces in a 17-module structure. There are three mutually exclusive sets of symbol patterns, or "cluster." Each cluster has 929 distinct patterns. Adjacent rows use different clusters, so it is possible for the decoder to tell if the scanning path is crossing row boundaries without the use of separator bars.

Every symbol includes at least two error-correction codewords. An option permits up to 510 additional error-correction codewords to be added to the symbol. There are three different data compaction modes that define the mapping between codeword values and decoded data.

What a Difference a Dimension Makes:
One-dimensional bar codes contain an access code that serves as a real-time key for opening a database. A PDF417 symbol contains a complete data record and requires no access to an external database. Data, text, graphics, biometrics and voice records are immediately applied to the application transaction by simply scanning the symbol.

PDF417 supports industry standard escape sequences to define international code pages and special encodation schemes. The capacity of PDF417 can be helpful in application where the data must travel with the label item, where a host database is not always available for quick look-up. PDF417 is being used for hazardous materials labeling; storing technical specifications and calibration data on electronic instruments; encoding fingerprints and photographs on the back of drivers' licenses.

PDF417 symbols require a 2D scanner; they cannot be read using an ordinary linear barcode scanner. A number of scanners are on the market using both laser and CCD camera technologies. PDF419 symbologies can be printed using laser printers or label printers on the market.