Guide · OtterPDF

Merge PDF files without uploading them

Combining PDFs is probably the most common document task there is. It's also the most common reason people end up sending private paperwork to a random website. You don't have to.

What you get

One PDF with every page from the files you added, in the order you chose, minus any pages you removed, with any sideways pages turned the right way. It's saved to your Downloads folder like any other download.

Steps

1. Open pdf.ottercraft.dev. Any current browser works, on a computer or a phone.
2. Add your PDFs. Drag them onto the page, or tap the drop area and pick them. You can select several at once, and you can add more later. New pages go after the ones already there.
3. Wait for the thumbnails. Every page gets a small preview so you can see what you're working with. Long documents take a moment; the counter in the header shows progress.
4. Put the pages in order using the arrows on each page. If you want whole files in a certain order, it's quicker to add them in that order to begin with.
5. Tidy up if needed: rotate a page that's the wrong way round, or remove a blank or duplicate one. This only affects the new file.
6. Press Download. The merged PDF is built on your device and saved with -edited or combined in the name. Your original files aren't touched.

Why nothing is uploaded

Everything OtterPDF does happens in code running in your browser tab. The previews are drawn by pdf.js in a background worker. The merged file is put together by pdf-lib from the pages you kept. No server is involved in either step. If you want to check, open your browser's developer tools and watch the network tab while you work. The page loads its own code and nothing else.

It also means there's no size limit from my side and nothing to "delete after 24 hours". When you close the tab, the files are gone from memory.

Things worth knowing

• Very large files. OtterPDF warns above 100 MB per file, because rendering hundreds of pages of high-resolution scans can use up a phone's memory. On a desktop it's usually fine. On a phone, merge in two passes.
• Password-protected PDFs can't be opened. Remove the password in the program that made the file first.
• Mixed page sizes are kept as they are. An A4 page and a US Letter page stay their own sizes in the merged file.
• Forms and links. Page content, images and vector graphics come through. Interactive form fields and links between pages may not survive a merge. If you need the form values to stay visible, flatten the form first.
• Offline works. Once you've opened OtterPDF once, it keeps working without a connection.

Related

• Split a PDF or extract specific pages
• Rotate PDF pages the right way up