You can use Automator - find these two functions Split pdf and Combine pdf pages. Use the Split function to “blow up” the document into individual pages delete the pages you need not in the new document Use Cobine pdf pages to stich the pages back again into the document. May be tedious and error prone with large documents. There is a whole lot of good pdf editors for Mac around, some of them do have free trials, so if you need to do this once, you can live with a free trial. Pdf Merging Online DC is a classical tool, but is now available only as a subscription. PDF Elements Pro works well, also Quoppa PDF Studio (both paid, but reasonably). There are also a few on-line pdf editors, some for free, thus if your document is not confidential or too personal, you can check the online things. Google around a bit.
To make sure I can use all the images, I’ve decided to use the process PDF Element to merge all the pages into a single image. Open a document with PDF element, and then click on “To Others”. You will see a pop-up window similar to the one below. Click on convert to Image. You could also choose copy Page to get a copy of the page. Click copy, and the image will be added together into a single image.