pocketbook 840 read only problem questions

I have read many topics about sd micro card not working, cloning, etc.
But i have some questions. I have a pocketbook 840 that works, but does not remember the page of the book. So this must a problem of the internal SD card.
I tried to repair the SD with some linux commands i found. that did not work.
I wonder if i use dd or any other tool to get an image, is this image any good?
Is the problem solely the SD card? Or is the image not good?
What i mean : if i go through the whole process, is the image i use any good?
Or do i need some new image?

And if the image is ok to use, could i format the sd card, and then rewrite the image? what exactly is the read problem? is this a hardware failure?

Then i also wonder if i clone the sd, why must i change the size with hex editor? will the clone not make a 16 GB card 4 GB again?

hope some expert can help me. anyway, thanks for reading!
Mark