Yes, you can! Attachments help our Pros out to understand what you are looking for, and references or extra information in the form of attachments is always welcome.
Keep in mind that for Voice, AudioAds, and Translation projects, you can add the script as an attachment for reference. However, the script must be pasted into the script portion of the project form. This is so the platform can count the number of words to be recorded, and we can charge you appropriately.