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Umm, are you sure you're asking this in the right support forum? Textastic doesn't include a PDF viewer. Maybe I'm missing something?
Are you trying to move local files into a different folder? Or are you talking about remote files?
Sounds like a good idea.

P.S.: Lange nichts voneinander gehört :)

Please send the details by email to support@textasticapp.com.

Can you please post a screenshot or point me to a specific file location and describe the problem you are seeing? 
Can you please send me the file to support@textasticapp.com? 5 to 8 seconds is indeed not acceptable in any way. I have not seen such delays in my own files.