Surely this has to be under consideration at Pipedrive? Can you update us on a timescale for this? Pipedrive and Dropbox would be a match in heaven :)
"Integration" covers a multitude of use-cases and requirements, especially between solutions as wide-ranging as Pipedrive and Dropbox.
Every user will have different needs and requirements, so a single 1:1 direct integration is a big ask.
The best solution is to use an workflow automation solution like Make (https://www.make.com). It's a highly visual workflow automation solution with pre-built connectors for over 1,500 services, including Pipedrive and Dropbox, covering pretty much all of the available API endpoints.
Make allows you to build your own workflows (in either direction) including if-then-else business logic and processing of arrays (like line items), iteration and aggregation - all without writing a single line of code.