A desktop publishing application from Microsoft that focuses on page layout and graphic design.
Considering that you're looking for a perpetual license to avoid losing access when your subscription expires or when Microsoft pulls the software from the 365 suite, your best option is to acquire a license for Office Professional 2021. This specific version includes Publisher and will remain functional on your computer indefinitely, though it will stop receiving security updates after the 2026 cutoff. You should note that Publisher was intentionally excluded from the newer Office 2024 perpetual release, making the 2021 edition the final available version for purchase.
AFAIK, Microsoft no longer sells Publisher as a standalone product on its primary storefront, you should be able to purchase the Microsoft Office Professional 2021 suite, which is a one-time purchase that includes Publisher alongside the core apps like Word and Excel. You can still find legitimate retail keys from authorized third-party sellers and established tech retailers like CDW or My Choice Software, where prices for the full suite often range between $200 and $400 depending on the specific licensing terms. Some specialized software vendors like Digital License and FastSoftwares still list individual keys for Publisher 2021 specifically, often at a lower price point around $50 to $100, though you should verify their current stock and activation guarantees before buying. Be careful with extremely low-priced "lifetime" deals on unfamiliar sites, as these are often volume licenses not intended for individual resale and may be deactivated by Microsoft later.
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hth
Marcin