Start by checking the file extension

The fastest way to figure out what opens a file is to look at the letters after the last dot in the filename. That's the file extension, and it tells you what kind of file it is. For example, a file named "budget.xlsx" has the extension .xlsx, which means it's a spreadsheet. A file named "photo.jpg" has the extension .jpg, which means it's an image.

On Windows, file extensions are often hidden by default. To see them, open File Explorer, click the View tab at the top, then check the box next to "File name extensions". On Mac, select the file, press Command+I to open the info window, and look for "Kind" — that tells you the file type.

Once you know the extension, you can search for what program opens that type of file. The most common extensions — .doc, .pdf, .jpg, .mp3, .mp4 — are usually opened by programs already on your computer. Less common extensions may need a program you don't have yet.

Key Takeaways

  • The file extension (the letters after the last dot) tells you what kind of file it is and what program should open it.
  • Windows hides extensions by default; turn them on in File Explorer under View to see them clearly.
  • Right-clicking a file and choosing "Open with" shows you what programs on your computer can open it.
  • If no program on your computer works, search the extension online to find a free program that handles that file type.
  • Never download a program from an unfamiliar website; stick to official sources like the program's main website or the Microsoft Store.

Try right-clicking and using "Open with"

The easiest next step is to right-click the file and look for an option called "Open with" (on Windows) or "Open with" (on Mac). This shows you every program on your computer that might be able to open that file type. Try each one until something works.

On Windows, you'll see a list of programs. Click one to try it. If it opens the file and displays it correctly, you've found your answer — you can right-click the file again and choose "Open with" then select "Choose another app" and check "Always use this app" to make it the default. On Mac, right-click the file, hover over "Open With", and pick a program from the list.

If "Open with" shows no programs at all, or if every program you try fails to open the file properly, the file type probably needs a program you don't have installed yet.

Search online for the file extension

Once you know the extension, open a web browser and search for the extension itself — for example, search ".dwg files" or ".psd files". The first few results will tell you what the file is used for and what programs open it. Look for programs that are free or that you already own.

Common file types have many options. A .txt file opens in Notepad, Word, or dozens of other programs. A .pdf opens in Adobe Reader, your web browser, or many other readers. A .zip file (a compressed folder) opens with the built-in tools on Windows or Mac without installing anything new.

If the extension is unusual or you're not sure which program to trust, look for the official website of the program that created the file. For example, if someone sent you a .psd file (Photoshop), Adobe's website will tell you that Photoshop opens it. If you don't own Photoshop, the search results will also show you free alternatives like GIMP or Photopea.

Download a program only from official sources

If you need to download a new program to open the file, go directly to the program's official website. Do not download from random websites that promise to open "any file" — these often contain malware or unwanted software.

For Windows, you can also use the Microsoft Store, which is built into Windows 10 and Windows 11. Search for the program name there, and you'll see official versions. On Mac, the App Store works the same way. Both stores check programs before listing them, so they're safer than downloading from an unknown website.

Once you've installed the program, right-click the file again, choose "Open with", and select the new program. If it opens the file correctly, set it as the default by checking the box that says "Always use this app to open this file type".

Handle compressed files and archives

Files with extensions like .zip, .rar, .7z, or .tar are compressed folders — they hold multiple files squeezed into one smaller package. Windows and Mac both have built-in tools to open these without downloading anything.

On Windows, right-click a .zip file and choose "Extract All". On Mac, double-click a .zip file and it will automatically extract. For other formats like .rar or .7z, you'll need a free program like 7-Zip (Windows) or The Unarchiver (Mac). Once you extract the files, you'll see what's inside, and you can open those files normally.

Never run a program directly from inside a compressed file. Always extract it first, then run the program from the extracted folder.

What to do if nothing works

If you've tried every program on your computer and downloaded a program from the official source but the file still won't open, the file may be corrupted or incomplete. Try these steps: first, ask the person who sent you the file to send it again — it may have been damaged during transfer. Second, check the file size; if it's very small (a few kilobytes) when it should be large, something went wrong during download.

If the file came from the internet, try downloading it again in a different browser. Sometimes a download stops partway through without telling you. If you downloaded it from email, try downloading it again from the email rather than opening it directly from the attachment.

As a last resort, you can upload the file to an online conversion service — many websites will convert files from one format to another for free. Search for "[extension] converter online" and you'll find options. Be cautious with sensitive files; only use converters you trust, and never upload files that contain passwords or personal information.

Frequently Asked Questions

What if the file has no extension?

Right-click the file and choose "Properties" (Windows) or "Get Info" (Mac). Look for the "Type" or "Kind" field — this tells you what the file actually is, even without an extension. Once you know the type, you can search for programs that open it. You can also try opening it with a text editor first; if it shows readable text, it's a text file.

Can I change a file's extension to open it in a different program?

No — changing the extension doesn't change what the file actually is. A .jpg file renamed to .png is still a .jpg file and won't work properly in programs that expect .png. The extension is just a label. If you need to convert a file to a different format, use a conversion program or online converter designed for that file type.

Is it safe to download programs to open unknown files?

It's safe if you download from the official website of the program or from the Microsoft Store or App Store. Never download from a website you don't recognize, especially if it promises to open "any file type" or asks you to disable your antivirus. Stick to official sources, and your computer will stay safe.

What does "file association" mean?

File association is which program opens when you double-click a file. When you right-click a file and choose "Open with" then check "Always use this app", you're setting the file association. You can change it anytime by right-clicking the file again and picking a different program.

Why do some files open in the wrong program?

This happens when a program you installed changed the file association without asking. For example, installing a new image viewer might make it the default for .jpg files. To fix it, right-click the file, choose "Open with", select the program you want, and check "Always use this app". You can also change defaults in Settings (Windows) or System Preferences (Mac).