How is this different from other online PDF tools?

Most online PDF tools send your files to a remote server for processing. This tool processes everything locally in your browser using client-side JavaScript. Your files are never transmitted to any server, which means your document content stays entirely under your control.

Are my PDF files uploaded?

No. Your files are read directly by your browser. Your files are never transmitted over the network. The tool works entirely within the browser tab you have open.

Can I verify that files are not uploaded?

Yes. Open your browser's developer tools (F12), go to the Network tab, and watch for any outgoing requests while using the tool. You will see no file data leave your browser. The site may record an anonymous page-view count, which never includes your files and can be disabled.

Does this tool work offline?

Yes, once the page has loaded the tool processes your files entirely in your browser; tool functionality needs no network connection. You can disconnect from the internet and continue using it.

What happens when I refresh the page?

Because nothing is stored on a server, refreshing the page clears your current session. Any files you had selected will need to be selected again.

Does this tool store my files?

No. Files are held in browser memory only for as long as the page is open. Closing or refreshing the page discards them. Nothing is written to disk by the tool, and nothing is sent to a server.

Can this tool unlock password-protected PDFs?

No. This tool does not attempt to remove or bypass PDF password protection. If you know the password, the Unlock PDF tool on this site can remove it locally; then this tool can process the file.

What technologies does this tool use?

This tool uses client-side JavaScript and pdf-lib to copy and alternate pages from both PDFs entirely within your browser — your files never leave your browser.

Does this tool use WebAssembly?

No. This tool uses client-side JavaScript and pdf-lib for local PDF structure editing. No WebAssembly is involved.

How do I interleave two PDFs with this tool?

Choose your first PDF (the fronts) in the first picker and your second PDF (the backs) in the second picker, then press the interleave button. The pages are alternated locally in your browser as A1, B1, A2, B2, and the result is offered as a download named interleaved.pdf.

My back pages came out in the wrong order — what should I do?

When duplex backs are scanned with the page stack reversed, tick the "reverse the second PDF" checkbox before interleaving. This flips the second document's page order first, so its last scanned page pairs with the first front instead of the last.

What happens if the two PDFs have a different number of pages?

Pages alternate one-for-one as far as both documents reach, and once the shorter file runs out, the remaining pages of the longer file are simply appended at the end. Both files are read into memory and processed locally with pdf-lib, so nothing is sent anywhere.

Does the Interleave Merge tool cost anything to use?

Interleave Merge is completely free — no account, no sign-up, and no limit on how many PDFs you interleave — and it always will be. Both files are loaded into your browser's own memory and alternated page by page (A1, B1, A2, B2…) entirely on your device, so your documents never leave your browser and no data is sent to any server.

Interleave Two PDFs Privately — Combine Fronts and Backs in Your Browser

Select two PDFs; their pages are merged alternately (with an option to reverse the second) and offered as a download — all processed locally in your browser.

Quick answer

What it does: Select two PDFs; their pages are merged alternately (with an option to reverse the second) and offered as a download — all processed locally in your browser.
Free?: Yes — 100% free, no account or sign-up.
Files uploaded?: No — everything is processed in your browser.
Works offline?: Yes — once the page has loaded.
Best for: Scan a double-sided document in two passes — fronts first, then backs — then interleave both PDFs to restore the correct reading order.
Good to know: If the two documents have different page counts, the longer document's extra pages are appended at the end.

How it works

Select the first and second PDF files from your device.
Both files are read into browser memory — no data leaves your browser.
Optionally reverse the second PDF (useful when back sides were scanned in reverse order).
pdf-lib alternates the pages (first, second, first, second…) and appends any remainder.
The merged PDF is offered as a download directly from your browser.

When to use this tool

Scan a double-sided document in two passes — fronts first, then backs — then interleave both PDFs to restore the correct reading order.
A legal secretary reassembles a duplex-scanned contract whose odd and even pages were saved as two separate scan files.
A teacher merges the front and back scan batches of a stapled class handout into one properly ordered PDF for distribution.
If the two PDFs have different page counts, the extra pages from the longer file are appended at the end, not interleaved.

Frequently asked questions

How is this different from other online PDF tools?: Most online PDF tools send your files to a remote server for processing. This tool processes everything locally in your browser using client-side JavaScript. Your files are never transmitted to any server, which means your document content stays entirely under your control.
Are my PDF files uploaded?: No. Your files are read directly by your browser. Your files are never transmitted over the network. The tool works entirely within the browser tab you have open.
Can I verify that files are not uploaded?: Yes. Open your browser's developer tools (F12), go to the Network tab, and watch for any outgoing requests while using the tool. You will see no file data leave your browser. The site may record an anonymous page-view count, which never includes your files and can be disabled.
Does this tool work offline?: Yes, once the page has loaded the tool processes your files entirely in your browser; tool functionality needs no network connection. You can disconnect from the internet and continue using it.
What happens when I refresh the page?: Because nothing is stored on a server, refreshing the page clears your current session. Any files you had selected will need to be selected again.
Does this tool store my files?: No. Files are held in browser memory only for as long as the page is open. Closing or refreshing the page discards them. Nothing is written to disk by the tool, and nothing is sent to a server.
Can this tool unlock password-protected PDFs?: No. This tool does not attempt to remove or bypass PDF password protection. If you know the password, the Unlock PDF tool on this site can remove it locally; then this tool can process the file.
What technologies does this tool use?: This tool uses client-side JavaScript and pdf-lib to copy and alternate pages from both PDFs entirely within your browser — your files never leave your browser.
Does this tool use WebAssembly?: No. This tool uses client-side JavaScript and pdf-lib for local PDF structure editing. No WebAssembly is involved.
How do I interleave two PDFs with this tool?: Choose your first PDF (the fronts) in the first picker and your second PDF (the backs) in the second picker, then press the interleave button. The pages are alternated locally in your browser as A1, B1, A2, B2, and the result is offered as a download named interleaved.pdf.
My back pages came out in the wrong order — what should I do?: When duplex backs are scanned with the page stack reversed, tick the "reverse the second PDF" checkbox before interleaving. This flips the second document's page order first, so its last scanned page pairs with the first front instead of the last.
What happens if the two PDFs have a different number of pages?: Pages alternate one-for-one as far as both documents reach, and once the shorter file runs out, the remaining pages of the longer file are simply appended at the end. Both files are read into memory and processed locally with pdf-lib, so nothing is sent anywhere.
Does the Interleave Merge tool cost anything to use?: Interleave Merge is completely free — no account, no sign-up, and no limit on how many PDFs you interleave — and it always will be. Both files are loaded into your browser's own memory and alternated page by page (A1, B1, A2, B2…) entirely on your device, so your documents never leave your browser and no data is sent to any server.