This week I helped a friend with an issue where her Windows PC “converted all of her PDFs into Google Chrome files.”

That’s how she worded the problem.

PDFs on her PC that previously had an Adobe Acrobat icon now showed Google Chrome icons, and double-clicking on them opened the files in Chrome.

I’ve seen this exact issue before, so I was able to talk her through it over the phone.

The problem was with the default app preferences.

Every computer — Windows or Mac — has an internal list of what default programs to use to open each file type.

Let’s use PDF files as an example.

For PDFs, your computer might open them with Adobe Acrobat or Acrobat Reader, or Apple’s Preview or a browser, like Google Chrome or Firefox.

Like my friend, sometimes you’ll open a folder and see strange icons on your files.

Usually this happens after a software update. In this instance, it was probably after an operating system or Google Chrome update.

To fix it, you’ll need to reset the default program for PDF files.

On the PC, right click on any PDF and choose “Open With” from the popup menu.

At the top of the window, you should see the app that’s currently set to open PDFs.

You’ll also see a list of any other app Windows can use to open PDFs, including all your browsers.

Pick the app you want to use to open PDFs from now on and then look at the bottom of the box to see a check box to “Always use this app to open .pdf files.” Click to put a check in that “always open” box and then click OK.

In an instant, you’ll see all the PDF files change over to show the icon of the app you choose. If you chose Acrobat, all the PDF files will now show with an Adobe Acrobat icon.

Mac users can use the same method. Pick a file, right click and choose Get Info.

In the Get Info window, click the arrow to expand the Open With section and you’ll see a popup menu with all your app choices.

Choose the one you want and then click the “Change All” button below and then close the Get Info box.

This advice isn’t just for PDFs. You can set the default app for any file type using these same instructions.