I need to remove the last three pages of a PDF before I send it. How do I do that without special software?

In Acrobat: Tools > Organize Pages, select the pages, click the trash icon and save.

Without Acrobat:
• Windows: open the PDF in Chrome or Edge, press Ctrl + P, set the printer to Save as PDF, choose Custom pages and enter only the ones to keep, for example 1-12.
• Mac: open the PDF in Preview, show thumbnails, select the pages, press Delete, then save.

Always save under a new name so that you keep the original in case you cut the wrong pages.

Preview did it in a minute. Thanks.