I think there is a practical limit on the data capacity of a Code 128 barcode, particularly when alpha characters are introduced. Encoding alpha characters can increase the barcode size by about 50% apparently. Use a 2D barcode if you need to store more than 10 characters.
If the barcode will include static data you can use the one of the 2D barcodes in Designer (PDF417, DataMatrix or QRCode). If the barcode will be encoded with data captured in a fillable PDF form, you can use the PaperFormsBarcode in Designer and choose from PDF417, DataMatrix or QRCode.
I suggest you use QR Code. QR Code can encode the most data compared with other barcode types. It can encode:
- numeric data (digits 0 - 9);
- alphanumeric data (digits 0 - 9; upper case letters A - Z; nine other characters: space, $ % * + - . / : );
- byte data (default: ISO/IEC 8859-1; or other sets as otherwise defined);
- Kanji characters. Kanji characters in QR Code 2005 can be compacted into 13 bits.
It depends what data you are trying to encode. Code 128 is mainly used for transportation, and ordering applications. It can hold any character in the ASCII character set as defined by Latin-1 (ISO-8859-1).
This link gives some good hints at choosing barcodes based on your needs. Designer/Acrobat support a good variety of 1 D barcodes, and in the 2D set, we support the Data Matrix, PDF417, and QR barcodes.