To change a thing from one form into another while keeping what it holds. Conversion preserves content and not always fidelity.
Latin convertere (to turn around, transform), from com- (together, thoroughly) + vertere (to turn); to change a thing's form while carrying its content across the turning intact.
To change a thing from one form into another while keeping what it holds. Preserving the content is the promise; preserving every nuance of it is not always kept.