Three descriptions of one file
A file has a name, a declared type and actual bytes. The extension at the end of the name helps applications decide what to expect. The declared media type can come from browser or operating-system information. The bytes are the encoded content that a receiving application must ultimately read.
Those descriptions can disagree. A PNG renamed holiday.jpg still has PNG content. Browser type information may follow the extension, so two apparently matching labels do not necessarily give independent evidence. A supported signature check provides a separate clue.
The purpose here is to establish a useful starting point for an upload problem. It does not need to tell the complete history of the file. Once you know the likely supported format, compare it with the destination's permitted list and decide whether the filename or the encoding needs attention.
What this checker recognises
The basic inspector covers common signatures for JPEG, PNG, WebP, GIF, HEIC and PDF. A recognised result is reported using the corresponding format name. JPEG files commonly use either .jpg or .jpeg, and the inspector treats those suffixes as matching the same detected format.
Recognition is deliberately limited. Office files, videos, archives, SVG and other formats are not comprehensively identified by this basic tool. An unknown result for one of those items is not a claim that the file is corrupt or unacceptable everywhere.
HEIF-family containers need particular caution. A recognised header alone cannot establish that every image inside will decode in this browser. If you need to convert a HEIC, use the dedicated converter and rely on its actual decoding result. The basic format label is not a conversion test.
How to use the result for an upload
Open the file workspace and select the intended copy. Enter accepted formats if the receiving site publishes them, then run the inspection. Read the detected format and any filename mismatch alongside the original name. The selected destination category does not supply a secret list of official requirements.
If the real format is accepted and only the extension is wrong, a correctly named copy may be enough. If the real format is excluded, use a genuine export into an accepted format. Renaming an unsupported source to an allowed suffix can leave the same rejection waiting at the next check.
If no format can be identified, return to the source. Confirm the download finished and that the original opens in its intended application. Ask the sender for an agreed-format export when necessary. Do not assign extensions at random until an icon changes.
A signature does not prove full validity
A signature is a recognisable pattern, often near the beginning of the file. It does not establish that every later byte is correct. A partial download can retain the header while losing much of the content. A file might therefore be labelled PDF yet fail when a PDF reader tries to parse its pages.
The basic inspector does not validate PDF structure. Use the dedicated PDF tools for additional parsing and page information, with the understanding that even those checks are bounded. Passing a parser is different from proving that a document is safe, complete or suitable for an official process.
The checker also does not detect every malicious construction. Keep ordinary precautions for unexpected attachments. A familiar format name is not a safety endorsement, and the tool should not be used to justify opening files from an untrusted source.
Interpret mismatch warnings sensibly
A mismatch can come from an innocent manual rename or a poorly chosen export filename. It does not establish intent. Describe the observation precisely: the name ends in one extension, while the supported signature suggests another. That is enough information to choose the next step without inventing a story.
Look at the final extension when a name contains several dots. A file called report.pdf.png normally ends in .png. File managers may shorten a long name or hide known extensions, so inspect the complete filename when something seems inconsistent.
Correcting a label leaves the content unchanged. Converting writes a new representation. Keeping that distinction clear avoids unnecessary quality loss and helps you explain what was done to the file if a colleague or recipient asks.
Choose a conversion that preserves what matters
For a photograph, conversion may be straightforward, but transparency, quality and colour deserve review. A PNG or WebP with transparent areas needs a background for JPEG output. A JPG-to-PNG conversion does not bring back detail already lost in the source JPEG.
For a document, prefer an export from the original authoring application where possible. An image inside a PDF remains image content; it does not automatically acquire searchable text. A rendered PDF page image does not retain interactive fields or links in the same way as the original PDF.
Make My Files Work exposes particular supported operations rather than a universal convert-anything function. If the recognised source does not have an appropriate conversion here, obtain a suitable copy elsewhere through an application you already trust. Do not assume that recognition implies editable support.
Check the saved output, then the destination
After creating a new copy, inspect that copy rather than the source again. Confirm the name, detected format and any required size or image dimensions. Conversion can change those properties, so the previous file's report cannot substitute for an output check.
Open the output in a suitable viewer and review the actual content. A successful signature match does not tell you whether a photograph is clear or a document includes every page. Keep the original until the receiving service has confirmed the submission.
If a correctly identified, permitted file still fails, investigate the exact message. Encryption, byte limits, image dimensions, browser state or account permissions may be involved. The format checker narrows one question; it does not reproduce every check a private portal applies.
Questions that come up
Can I check a file without sending its contents away?
Yes. The inspector reads the selected file locally in your browser. It does not upload those contents to our server. Your later submission to a different site remains a separate action.
Does unknown mean that the file is dangerous?
No such conclusion follows from this result. Unknown means the supported signature checks did not identify it. It may be another legitimate format, incomplete or otherwise unreadable. Assess its source and use an appropriate trusted application.
Why is the icon different from the detected type?
Icons can reflect filename associations configured on your device. They are useful for navigation but are not a byte-level inspection. Compare the detected content and complete filename before deciding which format you have.