Why does my Keynote look different on Windows?
Because somewhere between your Mac and their PC the deck was translated into PowerPoint, and translation changes things. Fonts get swapped, animations get approximated, effects get redrawn. Here is what changes, and the route that keeps the deck as you built it.
The direct answer
Windows has no Keynote. To open your deck there, someone exported it to .pptx, or the recipient dragged the .key file into a converter. Either way PowerPoint is now rendering it with its own fonts, its own animation engine and its own effects. It is a different file drawn by a different program, so it looks different.
The three things that change
- Fonts. The .pptx names your typeface; if the PC does not have it, PowerPoint substitutes one, and every text box reflows. Headings wrap, bullets collide with images.
- Animations and builds. Keynote-only builds and transitions have no PowerPoint equivalent, so they are approximated or dropped, and timings shift.
- Effects. Shadows, reflections, image masks and some transparency are rendered by PowerPoint's engine, not Keynote's, so edges, blends and layered images can look flatter or wrong.
The fix that keeps everything
Do not convert. Export the deck to HTML instead (File → Export To → HTML…), which Apple documents as keeping animations and builds, then host it and send a link. The Windows user opens it in Edge or Chrome and sees Keynote's own player: your fonts as drawn on your Mac, your builds, your video and audio. They cannot edit it, which for a client deck is usually the point.
On Linkdeck: zip the export folder, upload it, copy the link. Free for one deck for 3 days; Pro keeps the link permanent, lets you password it and replace the deck without changing the URL.
When you must hand over a .pptx
If the other side needs to edit the slides in PowerPoint, you need a .pptx and some rework. Use fonts that exist on both platforms (Arial, Georgia, Calibri), keep builds simple (appear, dissolve, move), flatten complex image effects to PNG before exporting, and open the result in PowerPoint on a PC before sending. Send the link alongside it so they can see what it was meant to look like.
Questions
Is it Keynote's fault or PowerPoint's?
Neither. The two apps have different font, animation and rendering engines, so a translated file is a different file. Any conversion between them is lossy in one direction or the other.
Does PDF solve it?
For static slides, yes: fonts are embedded and the layout holds. For builds, transitions, video and audio, no; a PDF has none of them.
Does the viewer need anything installed?
For a Linkdeck link, a browser only. No Keynote, no PowerPoint, no Apple Account, on Windows, Android, Mac or iPhone.
Upload the deck and open the link on a PC
Export to HTML, zip, upload. Free for the first deck.