Windows

Microsoft Word: File, then Save As (or Save a Copy), and choose "PDF" as the file type.

Any other program: File, then Print, and choose the printer called "Microsoft Print to PDF" instead of a real printer.

Google Docs, in a browser: File, then Download, then "PDF Document".

Mac

Any program: File, then Print, then the "PDF" button at the bottom left of the print dialog, then "Save as PDF".

Pages: File, then Export To, then PDF.

Keep it under 2 MB

When the program offers a choice of quality, export at "Minimum size" or "Reduce File Size" rather than the print-quality default.

A CV with a large photo or scanned pages is the usual reason a file goes over the limit; remove the photo or shrink it before exporting.

A plain text CV with no images is normally only a few hundred kilobytes, well under the limit either way.