Go to Settings → Apps → Default apps and search for .pdf. Select the file type, choose your preferred PDF viewer from the list, then double-click a saved PDF in File Explorer to check the change.
01Check the file you’re opening
Section linkIn File Explorer, choose View → Show → File name extensions. Look for .pdf at the end of the saved file’s name. Changing the extension only renames the file, so leave it intact. If the viewer you want is missing from the list in Settings, confirm it is installed and can open a PDF from inside the app.
02Test with a downloaded file
Section linkOpen a saved copy from its folder in File Explorer. A PDF shown in a browser tab can be using the browser’s own viewer. If your saved copy opens in the app you picked, the Windows association is working. Download another PDF and open it from its folder if you need to repeat the test.
03If only one PDF won’t open
Section linkTry another PDF you already know is readable. If that one opens in your preferred app, check whether the first download completed or try getting a fresh copy from the sender. For another file type, search for its own extension in Default apps. A .pdf change only applies to PDFs.
Sources & further reading
Put it into practice
Before you convert
A short checklist for choosing an image format and checking the result.
Download checklist (.txt)