Maximum open Documents? 150?

Document.close not free all resources, if Document opened from PDFStream.
there is PDFFileStream.Close() need to invoke after Document.Close().
otherwise file occupied.
and there is another choice:
u can use PDFMemStream instead. int this way, document saved in byte array.

okay, i could try pdfmemstream for opening pdfs.

but what about my example-code and loading bitmaps into documents? how can i avoid the EMFILE-Exception there?

Sorry for late reply.
To avoid the issue try looking at this demo project

About file limit: remember you're handling low resource devices.