In terms of how I do it, it's a complete debinding and running the individual pages through a scanner. I then store the pages away safely afterwards and keep them all sorted in order.
As far as the way I do it goes the pages themselves do not suffer much damage at all. After removing the outer cover carefully (honestly this tends to be the most destructive part of the process as some of those do not come off nicely, but thinner works like doujins have it generally be pretty simple to keep everything intact), you apply a good amount of heat to the binding glue to make it partially melt (via a hairdryer with a nozzle attached to concentrate the heat on the length of the book, or a microwave if you want though that tends to lightly wrinkle the pages) and then a light tug on the top and bottom ends will effortlessly remove the pages evenly. If you do it right the pages will be more or less completely intact with extremely minor damage on the very very edge where the glue was.
So, as far as keeping the original book intact as it came to you it's very destructive, in terms of the material inside, not destructive at all.