what is the best way to create an underline input

I'm creating a web form that renders as a PDF.  I'm pulling in a lot of values from a database to populate fields on the form.  There are some other areas of the forms that will require manual input once the form is printed out.  This is a legal form and the layout has to be exact.  For input areas of the form, I need to create underlines for where the user would manually enter signatures, dates, and even some of the inputs will pull the values from the database, but still need to be underlined areas in the document.  What is the best way to mimic this underline input areas using CSS?  I could add the underline character, but then if a value gets pulled into the document is would show like this "_______________ my text ________".  I don't want the line broken up  How can I achieve this using CSS and when a value is pulled in from the database it still looks good with the line not getting broken up?

Thanks.