To see filename extensions on a Mac, open Finder, choose Finder > Settings, select Advanced, and enable Show all filename extensions. This reveals suffixes such as .pdf and .jpg without converting or rewriting the files. If you only want to inspect one item, use its Get Info window instead.
The important distinction is between showing an existing extension, changing a filename, and converting the document itself. These are different actions. Revealing extensions helps you recognise files and spot naming mistakes, but changing a suffix is not a reliable way to change the underlying format.
Inspect one file before changing a global preference
- Select the file in Finder. Do not open it merely to find out its name.
- Choose File > Get Info, or press Command-I.
- Expand Name & Extension if that section is collapsed.
- Look at the full name and the Hide extension checkbox.
- To show that file’s extension, deselect Hide extension.
This is a useful starting point when two documents look alike or a file arrived with an unexpected name. Read the field carefully before typing. If all you need is to reveal the suffix, use the checkbox rather than editing the filename.
For example, imagine two files displayed as Budget when extensions are hidden. Their actual names might be Budget.pdf and Budget.xlsx. Showing the extensions distinguishes the names; it does not establish that either document is safe, correct, or from the expected sender. Treat these as illustrative filenames, not a tested result on your own Mac.
Understand why Hide extension may appear ineffective
Finder’s global option takes priority over individual hiding preferences. Apple documents that when Show all filename extensions is selected, every extension is shown, including files with Hide extension selected in Get Info. That apparent disagreement is expected behaviour, not evidence of a broken file.
To review the global setting, click a Finder window, then choose Finder > Settings > Advanced. Record the existing state before making a change. Enable Show all filename extensions if you want a consistent view across your documents. Disable it if you want Finder to respect each file’s individual setting again.
Afterwards, return to the folder and inspect the same item. If the labels on your macOS version differ, use the version selector in Apple’s linked guide. There is no need to run a Terminal preference command or reset Finder just to try this documented setting.
Rename the descriptive part, not the format suffix
Once extensions are visible, it becomes easier to accidentally select the suffix during a rename. When changing a document’s descriptive name, preserve the existing extension unless you have a specific, verified reason to repair it.
For instance, renaming Draft.pdf to Meeting-notes.pdf keeps the same suffix. Renaming Draft.pdf to Meeting-notes.jpg does not convert a PDF into a JPEG image. The application may then fail to open it or interpret the name differently from what you intended.
Apple recommends keeping the extension-change warning enabled. In Finder’s Advanced settings, select Show warning before changing an extension. Read any warning rather than automatically confirming it. This is a helpful guardrail, not a guarantee against every naming mistake.
If you accidentally changed a known extension, stop and check the original filename from a reliable copy or backup before restoring it. Do not repeatedly guess suffixes on your only copy. Make a duplicate first when troubleshooting an important document.
Convert a document using the application that understands it
If your actual goal is a different file format, use the relevant application’s conversion or export function. Apple gives TextEdit’s text-format conversion and Preview’s image conversion as examples. Check the available output formats in the application rather than assuming any arbitrary conversion is supported.
Keep the original document, save the converted result separately, and inspect the output before sharing it. Formatting, editable elements, transparency, or other features may not carry over as expected. Revealing extensions makes the resulting names clearer, but it cannot verify conversion quality.
If the problem is simply that a PDF opens in an unwanted application, changing the extension is the wrong fix. Follow the separate instructions for changing the default PDF application for one file or all PDFs.
Short troubleshooting checklist
- One file still shows its extension? Review both its individual Hide extension checkbox and Finder’s global setting.
- All extensions appeared at once? Check whether Show all filename extensions was enabled.
- A renamed file no longer opens? Compare its name with a trusted original before changing anything else.
- Need another format? Export or convert in the appropriate application and retain the original.
- Want to undo the display change? Restore the recorded global setting and any individual checkbox you changed.
Source: Apple’s instructions for showing or hiding filename extensions. Hiding an extension changes its display, not the file’s contents, and does not make a suspicious download trustworthy.
This tutorial is for educational purposes. Test changes carefully before using them in production. The site owner is not responsible for misuse, damage, data loss, or production issues.
