ICO, PNG or SVG: choose the deliverable before converting
A website icon, a Windows shortcut and a mobile app icon are different deliverables. Start with the destination’s accepted format, then prepare the artwork. Renaming an extension cannot change the bytes inside a file.
Use ICO when the destination asks for it
A Windows icon can carry several raster images inside one ICO. Keep an editable master and export only the sizes your destination needs. A PNG renamed favicon.ico remains a PNG; a misleading name can make troubleshooting harder even if one browser happens to display it.
Keep PNG and SVG masters for other uses
PNG is a useful transparent raster master; SVG preserves vector artwork. IcoJet accepts PNG, JPEG, GIF, BMP and WebP, not SVG input. Export a square PNG from your vector editor before converting. The resulting ICO contains pixels, not editable vector paths.
Prepare a small delivery checklist
Write down the destination, requested format, dimensions and filename before export. Open the downloaded file in a viewer that understands that format, then install it in the real destination. Keep separately named web, Windows and mobile assets rather than treating one successful preview as proof that every platform is covered.