In a text field dropdown list, can I make a part of the text use a different font?

 You cannot do font formatting in the dropdown list.  You would need to use a VB field script.  You would use a Choose script.  In this example, we will format an Address using a separate font for a portion of the address

Dropdown List Field
In this example, we will name this field "phAddress" (without the quotation marks).  Set this as a text field coming from user entry.  Set the user control type as a drop down list.  Set the field usage to hide the field.  Set the dropdown list up as follows:

Option 1|A
Option 2|B
Option 3|C

Field Script Field

In this example, we will name this field "Address" (without the quotation marks).  Set this as a text field coming from field scripting.  Set the field usage for Proof and Production.  On the field scripting tab, choose VB script and set up your script as follows:

Choose(phAddress, "A|<font face='FranklinGothic-Demi'>Big Company</font>\n123 Main St. Chicago, IL 60160|B|<font face='FranklinGothic-Demi'>Giant Company</font>\n123 Madison Ave. New York, NY 00000|C|<font face='FranklinGothic-Demi'>Best Company</font>\n123 Main St. St. Louis, MO 63033", "")

The script is saying:
if the phAddress field=A, then put
<font face='FranklinGothic-Demi'>Big Company</font>\n123 Main St. Chicago, IL 60160 in the Address field
AND
if the phAddress field=B, then put
<font face='FranklinGothic-Demi'>Giant Company</font>\n123 Madison Ave. New York, NY 00000 in the Address field
AND
if the phAddress field=C, then put
<font face='FranklinGothic-Demi'>Best Company</font>\n123 Main St. St. Louis, MO 63033 in the Address field
OTHERWISE
leave the field blank

Note - The value of the phAddress field is being read from the text after the "|" symbol for each option.
 
 
The example mentioned above is using three different fonts(not the one mentioned in the above description,the fonts applied in the example are just for testing purpose)