How can I combine several pages to a PDF file using Preview?

You cannot combine partial PDF pages into a single full page as Preview is not a PDF Editor. The Preview granularity is individual pages.

Apple's Pages does not open PDF documents.

What you might consider is copy/paste the content of those partial PDF pages into a Pages document. If the donor PDF has page numbers, and you remove the partial PDF pages from it by right-clicking on their respective PDF thumbnails, then the PDF you export from pages with the consolidated content will introduce a page number discontinuity when you merge that back into your donor PDF.

Another approach is if you have access to MS Word 16.31 or later, you can open the donor PDF in it and it will generate a Word .docx document. You perform the page consolidation there, the page numbers will be in order and you then Save As… the replacement PDF.

Apple chose not to ship a PDF Editor with macOS, or create one installable for free from the Mac App Store. They are giving you the operating system for free, and implementing everything that users want in the operating system would equally delay product rollout and very likely force Apple to charge for the operating system as they once did.

How much is your dinking around in Pages costing you if you have considered the cost of your time? You could purchase a PDF Editor for between 70 - 150 USD (or even borrow MS Word from a friend) and your page consolidation efforts would have been done much sooner. Apple knows this which is why they aren't offering a PDF Editor version of Preview (or for that matter, Pages).

johnnyquest1 wrote:

I've started dragging pages from Preview into Pages and arranging multiple per page in Pages, but it's tedious. I'm also having difficulty cropping each page when needed. The scanner software can do more; it's kind of ridiculous, looking at you Apple.

Apple doesn't read here in this user-to-user forum for feedback or suggestions. You can, however, let them know your thoughts that their software which is not designed for managing scans doesn't work as well as software specifically designed to do that does for this task:

Product Feedback - Apple