Questions: File Types & Extensions Explained

Question 1

You have a photo saved as 'photo.jpg'. You rename it to 'photo.txt'. What happens?

• A. The file is converted to a text document you can edit
• B. The file is now unreadable and its data is permanently lost
• C. The image data is unchanged, but your computer will try to open it as a text file, producing garbled output
• D. Nothing changes — the computer ignores the extension and detects the real file type automatically

Answer: (C)

Renaming the extension changes only the label — the bytes inside remain identical JPEG image data. But the operating system uses the extension to decide which program to open the file with, so it will launch a text editor, which cannot interpret image bytes and will display garbage. The file is not broken or lost; it's just mislabeled. Option A describes actual file conversion, which requires software. Option D is incorrect for most consumer operating systems, which rely heavily on extensions.

Question 2

A word processor offers 'Save As' and lets you choose between .docx and .pdf. What actually happens when you choose PDF?

• A. The extension is renamed from .docx to .pdf; the content is identical
• B. The program reads your document, renders it into fixed page layout, and writes a new file in PDF format
• C. A copy is made and stored in a special PDF folder on your computer
• D. The .docx file is deleted and replaced by a .pdf file with the same information encoded identically

Answer: (B)

'Save As PDF' is a conversion, not a rename. The software reads your document in its internal format, reinterprets the content as a fixed visual layout, and writes out a completely different file structure in the PDF format. The original .docx is unchanged. This is why the PDF looks identical on any device (fixed layout) but is harder to edit — the two formats store the same visible content in fundamentally different ways.

Question 3

A file extension is just a label — changing it is equivalent to converting the file to the new format.

• T. True
• F. False

Answer: False

This is the most common misconception about file extensions. The extension tells the operating system how to interpret and open the file, but has no effect on what bytes are actually stored inside. Changing '.jpg' to '.png' does not convert the image — it just misleads both the operating system and the user about the file's actual format. Real conversion requires software that reads the original format, interprets its structure, and writes a new file in the target format.

Question 4

On most computers, file extensions are used by the operating system to determine which program should open a file when you double-click it.

• T. True
• F. False

Answer: True

This is correct. The operating system maintains a registry or mapping of file extensions to applications — .pdf opens in a PDF viewer, .mp3 opens in a media player, .docx opens in a word processor. This is why extensions matter practically: without them, you'd need to manually specify which program to use every time. It's also why showing file extensions in your file manager is useful — it makes the labeling system visible and helps you understand what you're actually working with.

Question 5

Why can't you convert a file to a different format by simply renaming its extension? What would you need to do instead?

Model answer: Renaming the extension only changes the label the operating system uses to identify the file type — it has no effect on the actual bytes stored inside. The file's content is still encoded in its original format. To genuinely convert a file, you need software that can read the original format, interpret its structure, and write out a new file in the target format. For example, to convert a .docx to a .pdf, you'd use a word processor's 'Save As' feature, which performs the actual format translation.

Understanding this distinction prevents a common frustration: people rename files and wonder why they 'broke' them. The file isn't broken — it's mislabeled. The content is intact, just misidentified. The principle is that format is determined by how the bytes inside are organized and encoded, not by what label is attached. Extensions are a convenience for operating systems and users, not a definition of the file's actual structure.