Lengthen character limit for a hidden field

What is the type of the field you are hiding? I had some discussions with supoort on character limits in the past.

According to the engineering team, string field types have a limit of 256 across the board, as do numerical fields (with the exception of phone number which is 10).  The text field type has a limit of 3200. You may want to consider changing the field type to text if you are looking to store more than 256 characters in the field.

Thanks. The field is to pass the URL for custom PDF reports (for the sales people to see what the prospect received). It looks like I can't change it to text and keep it a hidden field. 

Oh wait, I CAN edit that but not in the form (in admin-->field management). Thanks!

No problem! Yep, field management is where you would change the feild type. Just be careful about changing the type if it syncs to SFDC or if you have values in the field already. Quirky things happen when changing the field type. :) Hopefully that takes care of the issue.