Facing the same problem but discovered That it only happens in the dual messenger whats app, when using the main whats app no issues. And PDF  files open normally From the main whats app it's working with all readersWith 2nd whatsapp, it is not worki...

Me too 

Unfortunately, After doing All of these steps, the problem remains the same. 

Unfortunately, After doing All of these steps, the problem remains the same 

Unfortunately, After doing All of these steps, the problem remains the same