DnD 3.5 Modern

I'm new to roll20 is there a way I can use a PDF of a character sheet that I have in a new campaign? If so will someone please tell me how I can add it to the game?

You could import it as an image but that will not make it a usable (fillable) PDF in the game. The Character Sheets forum is for character sheets that the community makes for each game system using CSS/HTML. If you would like a 3.5 Modern character sheet you could make one if you know HTML/CSS (and are a Mentor) or you could ask the community if someone is willing to make one.

Ah...kay well I have no knowledge with that type of stuff thank ya very much for the info

Once a character sheet is made it is a simple matter to use it in your game. Since it is based on 3.5 you could have someone duplicate the existing 3.5 character sheet and modify it for 3.5 modern.