How can a salesforce community user download salesforce files?

Are these documents actually being saved to the record using Chatter Files or "Notes & Attachments" or are you wanting to render a visualforce page as a PDF and let the user view, print and/or download?
If you're just rendering the documents and not saving to the record, two things have to happen for Community user to see a Visualforce page. You'll want to Enable Visualforce Page Access to the Community, by going to Communities > Manage Communities > Force.com > Public Access Settings > Enable Visualforce Page Access. Next, is adding the page to the profile(s) of the community user(s), by going to Setup > Manage Users > Profile > Profile Name > Visualforce Page Access > Edit then move the page from the left column to the right.
If you've enabled Chatter Files, Community users can only see files that were uploaded INTO that community. (i.e., when an internal user with a full SFDC license uploads/creates a file and adds it to a record, the community users can't see it, eventhough you've shared the file with "The Entire Company" AND the community users have access to view the record.)
If you're using Chatter Files, you'll want to use a Trigger on ContentDocumentLink to share it wih Community users. (This will add it directly into both the Files AND Notes & Attachments related list and not post to the Chatter Feed at the top of the record.) You'd want to include this line of code so when internal users create and attach the PDF, community users can see it: UpdateContentDocumentLinkVisibilityOnInsert on ContentDocumentLink (before insert) { for(ContentDocumentLink. l:Trigger.new)l.Visibility='AllUsers'; }
If you're still using "Notes & Attachments" here's some additional info if community users still can't view them: "For the Customer Community license, access to Notes and Attachments for most objects is enabled by default. If your users with a Customer Community license can’t access Notes and Attachments on accounts and contacts, contact Salesforce." from https://help.salesforce.com/articleView?id=users_license_types_communities.htm&type=0#fntarg_8