Gonzo, Documents by Readdle was free for a while, if it still is then it will let you see the interface as it is very similar to PDF Expert. Documents allows you to highlight text and make bookmarks only whereas PDF Expert allows you to add signatures, add and remove pages, add notes, text, stamps, symbols etc.
As for syncing, PDF expert syncs with the following:
Dropbox, Google Drive, SkjyDrive, Sharefile, Sugar Sync, Box, Office 365 SharePoint and Oxygen Cloud. In addition it will let you set up other WebDAV servers, FTP and SFTP Servers.