I partially puzzled out what you wrote. From past topic in June, the ftp is Duplicati storage Destination, and part of the post here is correspondence with them (looking at posted sig).
I don’t know how /home/st30335/backup/jemjom gets in. Maybe folder path on storage?
who is listed on their web site as CTO.
You won’t see Duplicati uploading pdf files. All files should be of the form shown, with dblock and dindex as necessary for the volume of changes backed up, and a dlist at the end with file details.
Note that you’re not really supposed to have to peek inside the .zip files, but you asked about it. Source file changes are in default 100 KB (max) blocks in dblock files, and a dblock has a dindex.
The backup process explained (simplified)
How the backup process works (technical)
Database and destination internals (developer level)
Channel Pipeline (developer level but details what I meant when I said asynchronous processing)