Hi Christian Jutten,
I'm sorry that you didn't receive a response to your post. They sometimes get lost in the shuffle, and I do apologize.
What you describes sounds like some font substitution issues. You can test that easily by converting with OCR disabled as described in this document: How to disable Optical Character Recognition. However, if your PDF file was created from a scanned document and doesn't have editable/selectable text, then the converted file won't contain editable text.
So, the quality of the conversion will depend greatly on the quality of the source PDF.
That said, I'm also happy to cancel your subscription and process a full refund for you.
Please let me know how you'd like me to proceed. Your response will show up in my email inbox, so I'll be able to address it directly (no worries about your response getting lost in the shuffle).
Best,
Sara