By default, any documents you upload to DocHub will be totally private which means the file cannot be seen by anyone else, and it's not "published" to the Internet similar to any cloud storage such as Google Drive or Dropbox. Only you can view it, and you would need to be logged in first.
When you upload a file to DocHub, you'll see a privacy toggle which will always be set to Private by default, and you can always change this privacy setting at any time by opening the file and clicking on the File menu button in the upper right corner and choose Permissions and Sharing. You'll also see several sharing options in that window such as adding collaborators and getting a Share Link. The article below explains more about the sharing options:
How do I share or download my edited PDF?
To find out how long your documents are stored in DocHub, please see this article:
How long are my edited PDFs saved in DocHub?
Even when you set a document as Public or give out the Share Link, a person would need to know the specific URL in order to see it, and no one would be able to make changes to it unless you share the document with a person and set them as a Contributor or Admin. The Public documents do appear on your public DocHub page, but someone would still need to know your DocHub username to find it.
For any documents created or owned by an organization in DocHub, the default Private setting is only private from users who are not members of your organization which means any members of that DocHub organization will be able to view the document.