Use the letter spacing options to adjust the amount of space between the letters in a word or group of words. LiveCycle Designer ES uses EM units of measure (proportional width of a letter m) to space letters. The minimum value you can enter is -1 000 (-1em). The maximum value you can enter is 10 000 (10em). The default value is 0 (no spacing). You must enter whole numbers; fractions are rounded off to the nearest whole number.
The Letter Spacing box displays Mixed when you apply different letter-spacing values within one or more selected objects.
See also 

To change the letter spacing of text