The PDF417 is a 2D barcode. It is based on stacked barcodes. The characters are coded in code words. A code word consists of 17 modules, which consist respectively of 4 strokes and 4 spaces.
The PDF417 is a very compact and flexible code with variable length. Up to 1108 bytes can be coded.
Error Correction Level:
PDF417 uses a differently strong error correction. It is used according to the code length. By use of less than 41 code words the Error Correction level 2 is used. From 41 to 160 code words ECL3 is used. From 161 to 320 code words ECL4 is used. From 321 code words ECL5 is used.
Example: PDF417 code with ECL2
Example: PDF417 code with ECL3
Example: PDF417 code with ECL4
Example: PDF417 code with ECL5