Very little in work is genuinely new and original. The huge majority of it is re-examined, revised, re-worked. A document used as a base for something else, a presentation template where you can borrow the formatting and graphics, a white paper where you can adapt the ideas: it makes sense to do this.
Working from a solid base that has already found acceptance is sensible, a productive use of your time and investment.
That’s not to say that we shouldn’t strive for something that starts from a blank sheet of paper. Sometimes it’s the only way to come up with something that’s fresh, exciting, or game-changing.
But in the day-to-day passage of getting things done, re-work, re-use and recycling is a good thing.
It’s not plagiarism, where you’re passing somebody else’s work as your own and plagiarising their intellectual property. Properly acknowledged, cited or quoted, someone’s work you have built on is generally the better for it.