PDFs and Common File Formats: Open, Save and Convert

In short

Every file has a format that tells the computer what kind of information it holds and which app should open it. This tutorial explains the common file formats you’ll meet, such as PDF, DOCX, JPG and ZIP, shows you how to see a file’s type, and teaches the most useful conversion of all: saving any document as a PDF. You don’t need to buy software for any of it.

Before you start

A file’s format is shown by its extension, the few letters after the final dot in its name, such as report.pdf or holiday.jpg. Windows and macOS hide extensions by default, which can make similar files hard to tell apart. Lesson 1 shows how to display them.

Formats you’ll see most often:

• PDF: documents that look the same everywhere, ideal for forms, letters and sharing. Opens in any web browser.
• DOCX: Microsoft Word documents, which can be edited. XLSX is Excel spreadsheets and PPTX is PowerPoint slides.
• TXT: plain text with no formatting.
• JPG (JPEG): photos, compressed to keep files small.
• PNG: images with sharp edges, such as screenshots and logos.
• HEIC: the space-saving photo format many iPhones use.
• MP4: video. MP3 is audio.
• ZIP: a “compressed folder” that bundles several files into one smaller file.

Key terms

• File format: the way information is arranged inside a file, such as text, a photo or a video.
• File extension: the letters after the dot at the end of a file name that show its format.
• Default app: the app your computer uses to open a format automatically.
• Convert: create a copy of a file in another format, such as a Word document saved as a PDF.
• Compress / extract: pack files into a ZIP file, and unpack them again.

Lesson 1: see file types and open them

1. Show extensions on Windows 11: open File Explorer (Windows logo key + E), select View > Show > File name extensions. On Windows 10, open the View tab and tick File name extensions.
2. Show extensions on a Mac: in Finder, choose Finder > Settings (or Preferences), open Advanced and tick Show all filename extensions.
3. Open a file: double-click it, and the default app opens it. To choose another app, right-click it and select Open with on Windows, or Control-click and choose Open With on a Mac.
4. Open a PDF: on Windows, Microsoft Edge opens PDFs by default; other browsers can too. On a Mac, PDFs open in Preview.
5. Open a ZIP file: on Windows, right-click it and choose Extract All. On a Mac, double-click it.

Checkpoint: you can see whether a file ends in .pdf, .docx or .jpg, and open it in the app you choose.

Don’t rename a file’s extension to change its format. Renaming photo.heic to photo.jpg doesn’t convert it; it just confuses the computer.

Lesson 2: save or convert a document to PDF

From Microsoft Word, Excel or PowerPoint

1. Open the document and choose File > Save As (or Save a Copy).
2. Choose where to save it, then change the file type to PDF.
3. Select Save. Your original document stays as it was; the PDF is a separate copy.

From any app that can print (Windows)

1. Press Ctrl + P to open the print dialog.
2. Choose Microsoft Print to PDF as the printer.
3. Select Print, then choose a name and folder for the new PDF.

From any app that can print (Mac)

1. Press Command + P.
2. Open the PDF menu at the bottom of the dialog and choose Save as PDF.
3. Name the file and choose where to save it.

Checkpoint: open the new PDF and check every page looks right. Paper documents can be turned into PDFs too; see scanning documents to your computer.

Lesson 3: other everyday conversions

1. iPhone photos (HEIC) on Windows: the Photos app on Windows can usually open them, sometimes after installing a free extension it offers from the Microsoft Store. To have an iPhone save in a more widely compatible format, open Settings > Camera > Formats on the iPhone and choose Most Compatible.
2. Save a photo as another format on a Mac: open it in Preview, choose File > Export, pick a format such as JPEG and save.
3. Make a ZIP file: select the files, right-click and choose Compress to ZIP file (Windows 11; on Windows 10 choose Send to > Compressed (zipped) folder), or Control-click and choose Compress on a Mac.

Beware of websites offering free online file conversion, especially for private documents: your file is uploaded to someone else’s server. The built-in methods above keep files on your computer.

Check that it worked

Create a short document, save it as a PDF, and email it to yourself. Open the attachment on another device, such as your phone: it should look exactly like the original. Then put a few files into a ZIP and extract them again.

If something goes wrong

• ”You’ll need a new app to open this file”: the computer has no app for that format. Check the extension, then look for an app in the Microsoft Store or Mac App Store, or ask the sender for a PDF.
• A PDF opens in the wrong app: change the default app in Settings > Apps > Default apps on Windows, or with Get Info > Open with > Change All on a Mac.
• The PDF looks different from the document: check the page size and margins in the print dialog, and use Word’s own Save as PDF for the most faithful result.
• A ZIP file won’t open: the download may be incomplete; download it again from its original source.
• An email attachment ends in .exe or another program extension you didn’t expect: don’t open it. Program files sent by email are a common way to spread malware.

For organizing your files once they’re saved, see our files and folders tutorial.

FAQ

Do I need Adobe Acrobat to open PDFs?

No. Web browsers such as Microsoft Edge, Chrome and Safari open PDFs, and Macs include Preview. Paid PDF software adds features such as advanced editing, which many people never need.

What’s the difference between DOCX and PDF?

A DOCX file is meant for editing in a word processor. A PDF is meant for reading, printing and sharing, and looks the same on every device.

Can I edit a PDF?

Many PDF readers let you fill in forms, highlight and sign. For bigger changes, edit the original document and save a new PDF, or use a PDF editor.

Is it safe to open any PDF?

Most PDFs are safe, but treat unexpected attachments with care, especially from senders you don’t know. Keep your browser and PDF reader updated.