Are online PDF tools safe to use?

Step by step

1. Open the tool. Open Merge PDF in a current browser on your computer or phone. You don't need an account or a sign-up.
2. Optionally watch the network activity. If you want to check for yourself, open your browser's developer tools and select the Network tab. Keep the tab open while you work.
3. Select your PDFs. Click “Select PDF files” or drag and drop two or more PDFs onto the page. You can add more files at any time.
4. Put them in order. Drag the files into the order you want, use the arrow buttons, or sort them by name.
5. Merge. Click “Merge PDF”. Your browser combines the files on your device, and nothing is uploaded.
6. Download and protect. Click “Download” to save the merged PDF. If you plan to email it, lock it with Protect PDF first and send the password through a different channel.

Upload-based sites vs. tools that run in your browser

On an upload-based site, your file travels to the company's server, gets processed there, and the result is sent back to you. For a while, a copy of your document sits on a computer you don't control. You depend on the site to secure it and to delete it when it says it will.

A browser-based tool works differently. The page loads into your browser, and your own device does the merging, compressing or encrypting. PDF4U works this way. Its pages are also blocked by a strict security policy from connecting to other websites, so a file can't be sent elsewhere by mistake. There is no account, so there is no profile that collects your documents. Details are on the privacy page.

A checklist for judging any PDF site

• Does it say where files go? Look for a clear statement on whether files are uploaded or processed in your browser. If the site gives no answer, assume the file is uploaded.
• Does it require an account? A sign-up links your documents to your identity. Ask whether the tool really needs one.
• What does it promise about deletion? A line like “files are deleted after a few hours” tells you the files were stored on a server. That may be acceptable, but it is a promise you can't verify.
• Does it use HTTPS? HTTPS protects the file while it travels to the site. It says nothing about what happens to the file after it arrives.
• What does the Network tab show? Open your browser's developer tools before you process a file. A large outgoing request about the size of your file is a sign the file was uploaded.

What a browser-based tool cannot guarantee

Keeping files on your device removes the server from the picture. It doesn't make your device safe. These risks remain:

• A lost or stolen device. Downloaded PDFs stay in your downloads folder. Use a screen lock, and delete files you no longer need.
• Malware. Malicious software on your computer can read your files whatever website you use. Keep your system and browser updated.
• Shared computers. On a library, office or family computer, delete your downloads and close the tab when you're done.
• Sending the file. Once you email a PDF, it is out of your hands. Encrypt sensitive files with Protect PDF before you send them.

Tools used in this guide

• Merge PDF
• Compress PDF
• Protect PDF
• Unlock PDF

Related guides

• How do I password protect a PDF?
• How to compress a PDF and keep it readable
• How to sign a PDF without printing it