How do you differentiate between a business expense and an investment for the purpose of profit reporting? As I understand it, in a company, profit will be invested, either into capital assets or into projects.
How do you distinguish between an expense, and reinvesting profits back into company projects?
For instance, if Pfizer makes \$100B in revenue, spends \$80B on business expenses doing so, then spends the remaining \$20B on research for a new drug, would they have made \$20B in profit? or \$0?
In economics profit is simply defined as total revenue minus total costs or:
$$\Pi = TR-TC$$
In your case if

Pfizer makes \$100B in revenue, spends \$80B on business expenses doing so, then spends the remaining \$20B on research for a new drug.

from economic perspective the profit would be:
$$\Pi= TR -TC = {\\\$}100B - ({\\\$}80B+{\\\$}20B) = 0B$$
So from economic perspective the profit will be zero. (However, note the economic perspective is not necessary the same as an accounting perspective - I mention that since you reference reporting, but in this case accounting profit would also happen to be zero if $20B$ is on accounts treated as cost).