Opposite of "summarize"

Stretched out: to extend, force, or make serve beyond the normal or proper limits; strain: to stretch the imagination; to stretch the facts; to stretch food to feed extra guests; to stretch money to keep within a budget.

I need to stretch out this paper to reach the ten page minimum.

I can't believe the manager just stretched out my two paragraph email into a 35 minute meeting.

Extend: to increase the length or duration of; lengthen;

I need to extend this paper to reach the ten page minimum.

I can't believe the manager just extended my two paragraph email into a 35 minute meeting.

Adding new material that only confers bulk and no substance can be described as padding. This works both in physical and figurative senses.

I need to pad this paper to reach the ten page minimum.

In your second sentence, where the form of expression changes, I don't think pad works. From least negative to most negative, you could use expand, inflate, stretch out, blow up.

how about elaborate

in the sense of v. to add details to, or expand?

Inflate (“To enlarge an object by pushing air (or a gas) into it; to raise or expand abnormally”) seems quite suitable. Also consider swell (“To cause to become bigger”), puff up (“To inflate with air”), and blow up (“To inflate or fill with air”).

Expound on or expound upon: This comes to mind for use in a situation where one wants to add considerable detail to information provided in a summarized form.

For example, I would like to expound on the information provided in this email.