Searching "PDF to JPG" or "MP4 to MP3" brings up dozens of free websites that will do it in seconds. Most people use them without a second thought, and most of the time nothing bad happens. But it's worth knowing what you're actually doing when you drop a file onto one of those pages, so you can decide when it's fine and when it isn't.
What happens when you upload a file
An online converter can't change your file inside your browser in most cases. Instead your file travels over the internet to the company's servers, gets converted there, and you download the result. That means, for a while at least:
- A copy of your file sits on a computer you don't control, often in another country.
- The company decides how long it keeps that copy and who can reach it.
- The file name travels too, and names often say a lot ("Passport scan.pdf", "Salary review 2026.docx").
Reputable services say they delete files after a few hours and protect them while they're stored. Many of them do exactly that. The point isn't that every online converter is dangerous; it's that you're trusting a stranger with the file, and you usually can't check what they actually do.
The FBI warning about fake converter sites
In March 2025 the FBI's Denver field office warned the public about fake free file converter websites. According to the warning, some sites that offer to convert files actually hand back a result loaded with malware, which can then be used to steal personal information such as passwords and banking details. The FBI's advice was in line with common sense: be careful with free tools you find online, keep your security software up to date, and report anything suspicious.
This doesn't mean the well-known converters you've used for years are fake. It means that "free converter" is a phrase scammers know people search for, so it pays to slow down for a moment before you upload anything, and especially before you run anything you download.
What to check before you upload
- Is it a site you recognise? A converter that's been around for years and is widely talked about is a safer bet than one you found through an ad a minute ago.
- Does the address start with https and look right? Watch for look-alike names with an extra letter or an odd ending.
- Does it say what happens to your file? Look for a privacy policy that says how long files are kept and that they're deleted afterwards.
- Watch out for fake buttons. Free sites often show ads that look like big green "Download" buttons. The real download is usually smaller and appears only after the conversion finishes.
- Check what you get back. Converting a picture should give you a picture, and a PDF should give you a PDF. If you asked for a JPG and you're handed an
.exe, a.zipyou didn't expect, or a prompt to install something, don't open it. - Never type passwords or card details into a site just to convert a file.
When online is perfectly fine
For a meme, a picture that's already public, a song cover or a menu you downloaded from a restaurant's site, a well-known online converter is quick and harmless. The worst case is that a copy of something already public sits on a server for a few hours.
Think twice when the file is:
- an ID, passport, bank statement, payslip or anything with your address or account numbers,
- a work document, contract or anything your employer would rather not see on a stranger's server,
- private photos, especially of children or of your home (photos can also carry hidden location details),
- large, like long videos, which take ages to upload and often hit size limits anyway.
Converting files without uploading them
Windows already does some conversions on its own, one file at a time:
- Pictures: open a picture in Paint, then File, Save as, and choose JPEG or PNG.
- Pictures or documents to PDF: print them and choose "Microsoft Print to PDF" as the printer.
- Word documents: if you have Word, File, Save as, and choose PDF.
Free desktop programs such as VLC (video and audio) and LibreOffice (documents) also work offline, with more steps and more settings.
Santra is another option, made for doing this quickly and often. It runs on your Windows PC and works offline: it never uploads your files, their names or their contents. Start dragging a file, tap Shift, and drop it on the format you want in the small orbit that appears under your cursor. The new file appears next to the original, and the original stays as it was. It handles pictures, video, audio, Word, Excel, PowerPoint and PDF files, and many files at once.
To be fair about its limits:
- It's Windows 10 and 11 (64-bit) only; there's no Mac, phone or web version.
- It doesn't convert PDF to Word or Excel.
- It isn't code-signed yet, so Windows SmartScreen may show a warning the first time: More info, then Run anyway. Download it only from santra.pro.
- The first 25 conversions or tools are free; after that Santra Pro is a one-time US$19.
The bottom line
Online converters aren't evil, and for public, throwaway files they're fine. The risk is in what you upload and where. Stick to sites you recognise, never run a file you didn't expect, and keep anything private on your own PC, where nobody else gets a copy.