If you have ever tried to use Dropbox with Pages, Keynote and Numbers for iOS, you have probably read about DropDAV somewhere on the Internet. DropDAV is a server that lets you access your Dropbox account over the WebDAV standard, which the iWork suite for iOS supports.
However, DropDAV is not free anymore. It costs $5 a month. Free alternatives are few and far between. I have found one - called Otixo - that will work well for most people. Read on for more details.
Otixo is a WebDAV service that has a pretty good free version.
Otixo lets you access many different cloud services (Dropbox, Google Drive etc) from one elegant-looking online portal. It costs $9.99 (one time) for a "Business" account that gives you unlimited bandwidth. But a "Personal" account is free.
With a Personal account, you can transfer up to 2 GB of data across these services per month. If you get one to use with iWork on iOS, you will count towards this limit every time you upload a copy of the file to Dropbox through Otixo.
The 2 GB limit is enough for me. Most people will be fine with it. You may need to get the paid account if you work with a lot of presentations or with unusually humongous documents and spreadsheets.
Otixo lets you upload files to any folder on your Dropbox. If you use it with Pages, Numbers or Keynote on your iOS device, it will not save to Dropbox automatically. You will need to manually save it now and then. But it's worth trying.
For more details, visit their website here and create an account here.