as presented or described in a document, written statement etc (in contrast to what exists in actuality)
on paper.
(Треплев:) Как легко, доктор, быть философом на бумаге и как это трудно на деле! (Чехов 6). (Т.:) How easy it is, Doctor, to be a philosopher on paper and how hard it is in life! (6d).