I creating an app that works like an DMS(Document Management System) so my client will be uploading PDF's, XLS's and DOC's.
You don't want to be uploading anything to Heroku, it has an ephemeral file system which is reset on restarts/deploys. Anything uploaded should be uploaded to a permanent file store like Amazon S3
https://devcenter.heroku.com/articles/dynos#ephemeral-filesystem