How to merge, compress or protect a PDF without uploading it

By the Docmend team · Updated 19 October 2026 · 5 min read

Is it safe to upload a PDF to an online tool?

It depends on the tool. Many online PDF tools send your file to their servers, do the work there, and send the result back. That can be perfectly fine for a menu or a flyer. For a signed contract, an ID scan, a tax form or a medical letter, you want to know three things first:

• Is the file uploaded at all, or does the work happen in your browser?
• If it is uploaded, how long is it kept, and is it deleted automatically?
• Who else handles it. Some services pass files to other companies to process them.

A tool’s privacy policy should answer all three. If it doesn’t, treat the file as uploaded and kept.

How to tell if a tool uploads your file

• Read the privacy policy. Search the page for “upload”, “server”, “stored”, “retain” and “delete”. A clear policy says which features send files and which don’t.
• Watch what happens when you add the file. An “Uploading…” progress bar that fills before anything else happens means the file is going somewhere.
• Try it offline. Load the tool’s page, turn off Wi-Fi, then run the task. If it still finishes and gives you the file, the work happened on your device.
• Prefer apps already on your computer for anything you wouldn’t email to a stranger.

Merge PDFs without uploading

On a Mac with Preview

1. Preview saves changes automatically. To keep the originals, choose File → Duplicate on each PDF first.
2. Open the PDFs and choose View → Thumbnails in each one.
3. Drag the page thumbnails from one PDF’s sidebar into the other’s. Command-click to pick pages that aren’t next to each other, and drag thumbnails to reorder them.
4. To add a whole PDF, drag its icon from the Finder onto the sidebar of the open document.

In your browser with Docmend’s Merge PDF

1. Open Merge PDF and choose two or more PDFs, or drop them on the box.
2. Put them in order with the arrows.
3. Click Merge. The combined PDF downloads straight away.

Are the files uploaded? The tool’s own answer: “No. Docmend merges the PDFs inside your browser, so the files stay on your computer.” The pages, text, pictures and form fields come across; bookmarks from the separate files are not combined into one outline. Need the opposite? Split PDF pulls pages out into new files and leaves your original as it is.

Before you merge: a quick checklist

• Name the files in order (01-cover, 02-proposal, 03-terms) so the merge order is obvious and easy to check.
• Take out pages you don’t need first, such as blank pages or an old draft of the terms. Fewer pages means a smaller file and less for the reader to wade through.
• Check for anything private that shouldn’t travel with the bundle, like an internal note or someone else’s details.
• Merge first, then compress. Compressing once at the end is simpler than compressing every file separately.
• Open the result and scroll through it before you send it. A page in the wrong place is easy to miss and awkward to explain.

Compress a PDF to email it, without uploading

On a Mac: open the PDF in Preview, choose File → Export, pick Reduce File Size in the Quartz Filter menu, and save under a new name to keep the original. Apple notes the result may be of lower quality than the original.

In your browser: Docmend’s Compress PDF runs in your browser, and its page says files stay on your computer. Choose the PDF, pick how much to compress, and click Compress PDF. Pictures are made smaller while text stays sharp. A file that is mostly text is already small and won’t shrink much, and Docmend never hands back a bigger file. We tested this on 19 public-domain PDFs (median 12.9% smaller at Recommended): see the PDF compression benchmark.

Password-protect a PDF

On a Mac: in Preview, choose File → Export (enter a new name to keep an unprotected original), click Permissions, and select Require Password To Open Document. You also set an owner password, and you can require it for printing, copying text or making changes. Click Apply, then Save.

In your browser: Docmend’s Protect PDF locks a PDF with a password using AES-256 encryption and lets you choose whether people can print or copy text. Its page says nothing is uploaded. Docmend never sees or stores the password, so it can’t be recovered: keep a copy of the original or note the password somewhere safe.

Want to send a PDF that can’t be edited? Permission settings are the tool for that: they control printing, copying and changes. They don’t hide what’s in the file, though. If the content itself is private, set a password to open the document as well.

Which option fits which task?

Need to delete pages or trim margins instead? Use Docmend’s Remove PDF pages or Crop PDF.

For how Docmend handles files across the extension, see the privacy policy and what stays on your computer. Signing the merged file yourself? See how to sign a PDF without Adobe. Sending it to a client to sign? See how to get someone to sign a document online for free.

Sources

• Apple Support: Combine PDFs in Preview on Mac, checked 2026-10-15
• Apple Support: Reduce the size of a PDF in Preview on Mac, checked 2026-10-15
• Apple Support: Password-protect a PDF in Preview on Mac, checked 2026-10-15
• Docmend: Merge PDF files
• Docmend homepage FAQ
• Docmend privacy policy

Related guides

• How to sign a PDF without AdobeSign on a computer or phone with apps you already have.
• How to get someone to sign a document online for freeThree ways to get a PDF, Word file or Google Doc signed by someone else.
• How to get client feedback on a documentThe free ways to collect clear feedback on a Doc, PDF, Word file or video.
• Do I need to give Docmend access to my Google Drive?No Drive permission screen. What stays in the browser.