System Storage gets filled

Hi,
I have the problem that my disk space fills up extremely as system files. I can no longer delete these. Now I have tried a complete reset. Except the standard apps is only the YAC Reader on the Ipad. At first I had about 120gb free. After about 15GB of comics, but now 70GB are occupied (again as Systemdata).
I import the data via file sharing (PDFs) and always in packages of about 1GB. I also get occasional errrors when importing on the Ipad and only a few of the comics end up on the iPad. Does anyone know how I can free up system memory?

What kind of PDFs are you importing? Make sure you enable the fast PDF processing option in the Settings tab.

Thx for the fast response, actually I have this enabled.

And something I noted today, too. I tried it with dropbox upload. Loaded 1G and it consumes 4 GB on the iPad. Everything as system data when I check in the settings the YACReader only has 46,7 MB.

Are the pdf books or comics?

They are comic magazines.... noted that when I convert them to CBZ, I don't get this Problem... So I guess it's a problem with PDFs.

It looks like it is a problem with the PDFs, for some reasong they are getting pre-rendered by the app and that take the extra space, it shouldn't be the case with most comics in PDF format.