Guide · updated 2026-11-01T00:00:00.000Z
How to Combine PDFs Offline
Offline, for this tool, does not mean the site appears from nowhere. The first visit needs a connection. The browser has to download the page, the styles, the scripts, and the small decryptor that opens password-protected files. After that download, a service worker stores those site files on the device. Your PDFs are not in that store. Combining them offline means the program is already here, and the documents are already on the device.
If the browser has no service worker, the tool still works while you are online, and it still does not upload the files. It cannot open again once the network is gone. The public site registers the service worker only on the production build. A development preview may not.
Load it before you need it
Open Merge PDFs without uploading them on a normal connection. Wait until Choose files is on the page. In Chrome or Edge you can use the install icon. On iPhone, Share, then Add to Home Screen, saves an icon that opens the cached site. Either way, the cache is the site, not a folder of your documents.
Then turn the network off, or enable airplane mode, and reload. The merge page should come back from the cache. If you see a plain message that you are offline and the page is not saved yet, the first visit did not finish. Turn the network on, load the page once, and try again. Do not expect a file you have never opened on this device to be waiting offline. Choose it from the disk, a download folder, or a USB drive the computer can already see.
The same cache covers split a PDF in the browser, rotate PDF pages privately, reorder PDF pages, and the pack builder. They are pages of this site, so they are stored with it.
What still works with no connection
Add the PDFs. Put them in order. Turn sideways pages. Leave out a range under Manage Individual Pages. Download one file. The suggested name is merged.pdf. Change it in the save dialog. The save dialog writes to your disk. It does not send the PDF anywhere.
The proof panel should show zero network requests for that assembly. That is the useful check, and it is stronger offline, because a request cannot succeed if the network is off. If the tool instead reports that it could not read a font or a script, the cache was incomplete. Turn the network on, load the page, and repeat. How to merge PDFs without uploading them walks through the same join while you are online. Merge PDFs without sending them anywhere is the check against a request that leaves this site.
Helvetica, Times, and Courier are built into the PDF library. A pack that uses those faces does not fetch a font. Inter, Source Sans, and Liberation Serif are files on this site. They are not part of the offline cache. If you are offline and a pack asks for one of those faces, switch the cover and body text to Helvetica, Times, or Courier and build again. Nothing is uploaded in order to fetch a font. The message on screen says the font could not be read from this site.
What the cache does not do
The service worker does not keep your PDFs. Closing the browser does not upload them either. The tool can keep a working copy in this browser so the same files are still there after you open the pack builder or reload. That copy stays on the device. It is cleared when you choose Clear all work, after a period of inactivity (30 minutes unless you pick another), or when the tab closes if you picked that option. Passwords are never stored. If you chose “session” and the tab is gone, the files are gone, even if the site itself is still cached. Add them again from disk.
A size limit still applies offline, because the limit is memory in the tab, not a server quota. A phone, or a browser that reports under 4 GB, warns above 15 MB or 80 pages and refuses above 40 MB or 2,500 pages. A laptop that does not report memory warns above 32 MB or 400 pages and refuses above 80 MB or 8,000 pages. A computer that reports 8 GB or more warns above 64 MB or 1,000 pages and refuses above 160 MB or 20,000 pages. There is no paid tier. A refusal offline is the same refusal you would see online.
Password-protected files can be unlocked in the browser if the decryptor was cached with the site. The password stays in the tab for that job. It is not written into the saved work and it is not sent. A damaged file still fails with a plain error. There is no server to send it to for repair.
When you are back online, the finished PDF is still only on your device until you choose to send it. Use the channel the recipient already gave you. Combining the drafts did not require an upload. InHousePDF is not a professional adviser, and it does not decide which documents belong in the file.
Questions
Are my files uploaded?
No. The PDF is read and processed in this browser. It is not posted to a server. While the file is built, the proof panel counts network requests. That count should be zero. With advertising off, the page is not allowed to connect to other sites.
Does it work offline?
The first visit needs a connection, so this site can download. After that, a service worker keeps a copy of the site on the device. That copy does not include your PDFs. You can open the tool again with no connection and work on files already on the device. If the browser has no service worker, the tool still works while you are online, but not offline. Assembly does not call a server either way.
Is there a size limit?
Yes. The limit keeps the tab from running out of memory, and it depends on the device. It applies to the total size and page count of everything you have added. A phone, or a browser that reports under 4 GB of memory, warns above 15 MB or 80 pages, and refuses the job above 40 MB or 2,500 pages. A laptop or desktop that does not report memory, or reports from 4 GB up to but not including 8 GB, warns above 32 MB or 400 pages, and refuses the job above 80 MB or 8,000 pages. A computer that reports 8 GB or more warns above 64 MB or 1,000 pages, and refuses the job above 160 MB or 20,000 pages. There is no paid tier that raises the limit.