You cannot directly upload a PDF or word document into your guide/ You can however save the file into a document storage service such as Dropbox or Google Drive then add that file link to your guide as you would with any type of external link, as described here.
Dropbox and Google Docs are very easy to use but If you need any help, please submit a ticket through the Help & Support > Contact Us page in your account.
A few other options:
Convert the manual from a PDF to JPEG images and upload each image as a topic. How to upload photos.
If the manual is mainly text, simply copy and paste the text into a topic. You can still add photos to the topic as normal.
Find a video that could replace the manual, and then also link to the manual in the topic. How to add videos.