How to allow an applicant to download a document, fill it out, and upload the completed document in a single process element:
You wish to know what the best practice is to create a content item where applicants can click a file and download it, then upload it back into the same process element once complete.
A possible solution:
You can find a quick video detailing a possible solution attached it to this article below.
It is important to note, that to use the feature I have included in the video, the document will need to be hosted somewhere so that it has a URL.