Hi Paul,
Are you putting your files in the Quick File Receipts folder? They should sync within a few minutes (typically no longer than 5 minutes).
Also, check the file extensions, full list here:
http://community.quickfile.co.uk/t/dropbox-integration-setup/8931#4
To answer your question regarding multiple accounts, check out these instructions:
http://community.quickfile.co.uk/t/dropbox-integration-setup/8931#5
Hope that helps!