Highlight PDF Without Style Loss

I need to add colour-based highlighting to an existing PDF that was originally exported from Microsoft Word, but every piece of highlighted text—body copy, headers, and even footnotes—must keep its current font family, weight, size, and spacing exactly as they are now. No substitutions, reflows, or unexpected style shifts can slip in during the process.

The source file is a clean PDF; I can also provide the original .docx if that helps you work nondestructively. Once the work is finished I expect a PDF that:

• Displays the highlight colour I request on all specified passages
• Matches the original typeface and point sizes pixel-for-pixel throughout the document
• Prints and opens on any standard reader with no font re-embedding warnings.