You can extract the images, but they may have been compressed when inserting into the PDF.
A lot of print shops will only send you PDFs if you are paying for desktop publishing so that if you need edits you have to go back to them. It's shitty, when I worked retail I gave the customers all the files if they wanted them. The shop probably knows exactly what they are doing, if they didn't they would be using Office files instead of Adobe.
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