Need a PDF merged, an iPhone photo turned into a JPG, or a video made small enough to email? You search for it, click the first free site, drop your file in, and download the result.
Most of us never think about what happened in between. With many online converters, your file was uploaded to someone else's server, processed there, and stored for a while. For a meme, who cares. For a passport scan, a salary slip, a signed contract or a medical report, you probably should.
The good news: modern browsers are powerful enough to do most of this work on your own device. And you can check which kind of site you're using in about 30 seconds.
The 30-second check: is this site uploading my file?
You don't need to be a developer for this. It works in Chrome, Edge, Brave and Firefox.
- Open the converter site.
- Press F12 (or Ctrl + Shift + I; on a Mac, Cmd + Option + I) and click the Network tab.
- Drop a test file into the tool and run it.
- Watch the list of requests. If you see a request that takes a while and is roughly the size of your file, often marked POST or "upload", your file just left your computer.
Even simpler: the airplane-mode test
- Open the tool and let the page fully load.
- In the Network tab, change the "No throttling" dropdown to "Offline". Or just switch off your Wi-Fi.
- Now try the tool.
If it still works with no internet, the work is happening on your device. If it spins forever or shows an error, it needs a server, which usually means your file goes there.
(One fair exception: some AI tools download their model the first time you use them. Run them once while online, then do the offline test.)
7 everyday file tasks you can do without uploading anything
1. Remove the hidden location from your photos 📍
Phone photos usually carry EXIF metadata: the camera model, the date, and often the exact GPS location where the photo was taken. Some social apps strip it, but email attachments, cloud links and "send as file" usually keep it.
Before you send photos of your home, your kids or your new apartment to a stranger, strip the metadata. → Remove photo metadata
More on what's hidden in a photo: What your photos reveal: EXIF metadata and how to remove it
2. Redact a PDF properly, not with a black box 🕵️
This one catches lawyers and governments regularly. Drawing a black rectangle over text in a PDF only hides it visually. The text is often still there underneath.
Test it: open the "redacted" PDF, select the area under the black box, copy, and paste into Notepad. If the text appears, it was never removed.
A real redaction tool deletes the text from the file itself. → Redact PDF
3. Convert iPhone HEIC photos to JPG 📱
iPhones save photos as HEIC by default. They're great for storage, but plenty of websites, government portals and older Windows apps refuse them. Converting is a two-second job and doesn't need a server. → HEIC to JPG
4. Shrink a PDF to fit an upload limit 📄
Job portals and exam forms love limits like "max 2 MB". Scanned PDFs are usually huge because each page is a full-size photo. Compressing those images is what actually brings the size down. → Compress PDF
If a file refuses to shrink, this explains why: How PDF compression actually works
5. Sign a PDF without printing it ✍️
No need to print, sign, scan and email again. Draw or type your signature and place it on the page. → Sign PDF
6. Merge scanned pages into one PDF 📎
Forms often want "one PDF with all documents". Combine them in the right order in a few seconds. → Merge PDF
7. Make a video small enough to send 🎬
Phone videos are huge because of their bit rate, not their length. Lowering the resolution and bit rate a little usually cuts the size a lot while still looking fine on a phone. → Video Compressor
Why this works: Compressing a video without ruining it
Bonus: generate passwords locally 🔐
A password generator that runs on a server could, in theory, log what it generated. One that runs in your browser uses your device's own secure random number generator, and nothing is sent anywhere. → Password Generator
"Runs locally" doesn't mean "trust blindly"
To be fair: a site that processes files in your browser still sends your browser its code. You're trusting that code. That's exactly why the checks above matter. Don't take any site's word for it, including mine. Open the Network tab and look.
A few habits that help no matter which tool you use:
- Use a test file first when trying a new site.
- Be extra careful with ID documents, bank statements and medical files.
- Check the result before you send it: open the PDF and try copying "redacted" text.
- Prefer tools that work offline for anything sensitive.
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