How can I merge & compress pdf before the deadline?

I have several PDFs to combine into one smaller file for a submission due tomorrow but the free tools I tried either kept the size too big or scrambled the pages. How do I merge and compress them fast on my laptop?

Rename the files 01, 02, 03 first so the order stays obvious, and keep the originals. On a Mac, open them in Preview, show thumbnails, drag pages into one document, then Export with “Reduce File Size.” On Windows, Word can insert the pages and save as PDF, with picture compression enabled. Check every page before submitting because I learned the hard way that compression can blur signatures and receipts.

Free tools that make files bigger, classic. On a Mac: open everything in Preview, drag the pages into one file, then Export with the Quartz filter set to reduced size. On Windows I’d print the merged file to Microsft Print to PDF and pick lowest quality. What laptop are you on?