Windows File Explorer supports wildcard-based searching, which allows a user to locate files even when only partial information about the file (such as its extension) is known.

• * (asterisk) is a wildcard that stands in for any number of characters, including zero characters.
• ? (question mark) is a wildcard that stands in for exactly one character.
• Typing *.ext (for example *.pdf, *.docx, or *.jpg) in the search box tells File Explorer to match every file that ends with that extension, regardless of what the file name itself is.

To use this feature: open File Explorer, navigate to (or select) the folder you want to search — or search "This PC" to cover the whole drive — click the search box in the top-right corner, type the pattern such as *.pdf, and press Enter. File Explorer will scan the current folder and all its subfolders and display every matching file, along with its location, size, and modified date.

Why the other approaches are less suitable here:

• Recycle Bin only stores files that have been deleted; it is not a general-purpose search location for existing files.
• Simply browsing through File Explorer folder by folder is time-consuming and impractical in a "large directory" with many files and subfolders, since the file name is unknown.
• The dir command (in Command Prompt) can technically achieve something similar using dir *.ext /s, but it requires knowledge of command-line syntax and is not the standard, user-friendly way most users locate files in a GUI environment — the question is specifically about the File Explorer search box mechanism.

Hence, using the *.ext wildcard in the File Explorer search box is the most direct, efficient, and beginner-friendly method to find a file with a known extension but unknown name.