Is it a workbook for the LearnDash Course or just a resource?
One Way to add materials to the course is to add it to the course description but have it show up ONLY to students.
Remember there are shortcodes in Learndash [visitor] [/visitor] and [student] [/student]
If you add direct links to the pdf files in the media library and any other appropriate text between the [student] tags. It only shows up for people who are registered for the course.
If it’s a generic doc related to the course. You can ALSO or in addition – add the file as a download file in the courses EDD download settings. This makes it available in the persons purchases tab where they can see any downloads associated with the course purchase. This is not as elegant so I’d add it to the course description using the tags.
If you are unsure about the student tags, the WordPress editor has a button that embeds all of the learndash tags directly in any post.
If it’s just a pdf download you want to give away in exchange for an email address create a simple lead page/optin box or add the FREE Downloads Plugin for EasyDigitalDownloads that allows people to basically buy the download free in exchange for registering. Here’s an example of that approach at: https://campus.wpblogsupport.com/checklists/