Pdf with mainly black squares, special characters are displayed

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Hallo,

I received a pdf file. When I open it, the coverimage is as it should be, but the pages (1300) of the whole file (160 MB)) are littered with mainly black squares, special characters and embedded images are displayed only. 

I tried compatibility modus for Windows 7, still trying to convert to a word document (since 2 hours runtime), all to no avail.

The calibre e-book reader interestingly can read the file and displays the characters but in a very terrible design. All other software like pdf24, among others showed up the black squares as well.

What can cause this behavior and how can I overcome this that the file is readable in Adobe reader?

Regards,

Juergen