PDF files not readable from read only usb-stick

Hi, 

I work for a content company. We have published a read only usb-stick containing PDF files of our published magazines for our subscribers. However, we have some difficulties in opening the files on the stick. The stick has been created by a company specialized in creating read only usb sticks. But, when we try to open the PDF files directly from the stick, we get the following error:

Adobe Reader could not open … because it is either not a supported file type or because the file has been damaged (for example, it was sent as an email attachment and wasn’t correctly decoded)

But when we copy the same files from the usb stick to the harddisk, there is no problem in opening the PDF. Even more strange: the problem of not opening files directly from the usb-stick seems to occur randomly, depending on the version of Adobe Acrobat Reader used. For instance, the opening error occurs in the newest Adobe Acrobat Reader version  2021.007.20009 (64-bit), but not on on older versions, for instance Adobe Reader 2017.011.30204 (32-bit). 

To make things a little bit more complicated: the PDF files on the usb stick can be opened in any other PDF compatible program, such as Chrome, Firefox and many of the other PDF readers like Sumatra PDF, but just not the latest Adobe Acrobat versions. 

There is no file size difference in files on the usb stick and the hard disk, they both have the same properties. 

Any help or guidance on fixing this problem would be much appreciated. We can't force our readers to use a specified version of Adobe Reader, they should be able to open the files in any version of Adobe Reader. 

Best regards,

Mark