Is linking necessary to download files?

[Cross-linking for reference: https://stackoverflow.com/questions/34603685/how-to-download-files-to-app-from-app-folder-without-linking-an-account-via-drop ]

Based on the additional information you posted in your StackOverflow question, it sounds like you just want your app to connect to your own Dropbox account, as opposed to the accounts of your end-users.

The API was designed with the intention that each user would link their own Dropbox account, in order to interact with their own files. However, it is technically possible to connect to just one account. The SDKs don't offer explicit support for it and we don't recommend doing so, for various technical and security reasons.

However if you did want to go this route, instead of kicking off the authorization flow, you would use an existing access token for your account and app. (Just be careful not to revoke it, e.g. via https://www.dropbox.com/account/security .) Also, note that while embedding an access token isn't great, you definitely shouldn't embed your username and password.

For reference, here are some other similar questions on StackOverflow where I've posted answers:

https://stackoverflow.com/questions/15014001/allow-dropbox-api-to-access-my-account-on-users-device
https://stackoverflow.com/questions/27834922/auto-login-dropbox-account-on-core-api-without-login-prompt