If you would like to attach a file to any of your articles, you can easily do so inside your content editor. Here is how.
Open the article editor of your help center to create a new article or edit an existing one. Click somewhere inside the content to place the text caret. This would show you an icon to expand the editor side toolbar.
Click on that icon and it will show the various content blocks supported.
From the presented options choose File. This would open up a modal with all your uploaded files and a button to upload new ones.
To place an existing file, you have already uploaded before, in the editor, find it in the Attachments modal and click on the arrow down icon in front of its name.
To upload a new file, click on the Upload New button and choose the file you would like to insert. Wait for the upload to complete. Once the file has been uploaded and you can see it in the attachments manager, click on the arrow down icon at the leftmost of the file item that you just uploaded. This would insert the file inside your article as an attachment that could be downloaded by anyone with sufficient permissions.