Numbering makes the document's structure legible before anyone reads a word: four sections, in this order. On a technical resume — where a reader is looking for a specific thing rather than reading top to bottom — that ordering cue is worth more than a decorative flourish would be.

The double rule is the same idea. It is thin enough not to shout, but it reads as a deliberate drafting convention rather than a default underline, which is what keeps the page from looking like a Word document with a border switched on.

The frame is a real commitment. It runs at the sheet edge, so a printer that enforces its own margins will crop or shrink it, and the design is worth less without it — send the PDF. The numbering also assumes your sections stay in a sensible order; a resume with nine sections numbered to 09 starts to look like a form.