So, you don't want to keep the paper manual or you don't trust that you'll be able to find it again when you need it. Or you're just a digital hoarder like me. Either way, here's a search path to follow…
1. The manufacturer's website
This wasn't always such a viable option, but these days, if the manufacturer has a website and the product is from the last 10 years or so, there's a decent chance the website has the manual as a PDF. It may be on the product page, in the support section, or on an affiliated replacement-parts website.
If the product is discontinued and has been removed from the website, a trip through the Wayback Machine might get you to where you need to be. They started archiving PDFs awhile back so if you do find a manual link on the archived page, there's a decent chance it'll work.
2. Amazon (and other retailers—that part added 2024-06-09)
You don't need to buy (or have bought) it from Amazon, but if you can find their listing (or listings) for the product, they may have the manual PDF in the boring-product-details section shortly before the reviews. (Or somebody might have scanned or photographed the manual and posted it in the customer images, which may be sufficient for your needs.)
If you can't find a product listing, you might also try searching Amazon's PDF-hosting servers directly via your favorite search engine:
site:images-na.ssl-images-amazon.com filetype:pdfsite:m.media-amazon.com filetype:pdf
[added 2024-06-09] Home Depot and Lowes also have been known to host PDF manuals for products they sell.
For Lowes, you can do a similar site: search as above, with site:pdf.lowes.com.
3. The FCC
Products that use RF communication (wireless keyboards/mice, anything with a Wi-Fi or Bluetooth radio, etc.) that are sold in the US have to be registered with the Federal Communications Commission. The FCC issues an ID number to each such product, and maintains a database of exhibits submitted with the application—which can include the manual, teardown photos, and other goodies.
There are independent websites that let you search for a product by FCCID, or for its manufacturer and then browse through their registered products. Here's one I've used to find the manual and teardown photos (“internal photos”) of my wireless mouse.
(Not every submission includes the manual, so whether you'll be able to find the manual this way depends on the manufacturer and possibly other factors.)
4. The Internet Archive
Searching the Archive for such things can be tricky, but I just found a manual I'd failed to find on a few previous attempts on there, so it's worth a shot.
