How do I switch app to save the scanned PDF to my linked Dropbox account instead of uploading to cloud?
Sorry for the delay in response.
Currently, there is no option to switch the option to save PDF from Document Cloud to Dropbox.
However, you can save the files to Dropbox using "Share file" option.
Refer this Working with Scanned Documents — Adobe Scan Help help document for more information.
Let us know if you have any questions.