Interleave PDF Pages
Combine front and back scans into one PDF. Pages alternate from each set, and reversed backs from a flipped stack are put back in order.
Select PDF filesor drop them anywhere on this page, or paste
Opens in your browser. Nothing is uploaded.
Interleave PDF Pages, free and private
Interleave PDF combines front and back scans into one document with the pages in reading order. A scanner that only feeds one side gives you two files, one with every front and one with every back. This tool alternates pages from the two files, so you get front 1, back 1, front 2, back 2 and so on.
It also merges odd and even pages kept in two PDFs, or one PDF that holds all the fronts followed by all the backs. The backs can be reversed for scans made by turning the stack over, and a preview shows the new order with thumbnails before you save. Everything runs in your browser, so your scans are never uploaded.
How to interleave PDF pages
- 1
Add your fronts and backs
Press Select PDF files and pick two PDFs, the fronts first and the backs second. If one scan holds every front followed by every back, add only that file. With two files, file 1 is the fronts and file 2 is the backs, and the arrows under each file swap them.
- 2
Tell the tool where the backs start
With a single file, enter how many of the first pages are fronts. The box starts at half the page count, rounded up, so a 20 page scan splits into 10 fronts and 10 backs and a 21 page scan into 11 fronts and 10 backs.
- 3
Set the back page order
Keep Reverse the backs on if you turned the stack over to scan the second side. The scanner then reads the last back first, and the tool puts it back in place. Turn it off for a file of even pages that is already in order.
- 4
Interleave the PDF pages and check the order
The Page order preview shows thumbnails of the first 24 pages of the result. Each one is labelled Front or Back with its page number in the file it comes from. Change an option and the preview updates. When the order looks right, press Interleave pages, then Download PDF.
Why use PDFToolz for this
Two files or one
Use a fronts PDF and a backs PDF, or one PDF with the fronts first and the backs after them. The single file mode lets you set the exact page where the backs begin.
Reversed backs fixed
A one-sided document feeder usually returns the backs of a flipped stack last to first. Reverse the backs is on by default, so the last page of the backs PDF is paired with front 1.
Uneven page counts handled
If one set has more pages, you choose what happens. The extra pages can go at the end in their own order, or each one can get a blank partner page of the same size so the file still prints double-sided correctly.
Original quality
Pages are copied into the new PDF, not rendered again. Scanned images keep their resolution, an OCR text layer stays searchable and each page keeps its size and rotation.
No upload, no account
The files are read and rebuilt by JavaScript on your device, so no copy of your scans sits on a server. There is no watermark and no page cap. A very large scan is limited only by the memory of your device.
How to combine front and back scans into one PDF
A scanner with an automatic document feeder that scans one side at a time is the usual reason for this job. You scan the stack face up, turn it over, and scan it again. That gives two PDFs. Here is what happens to a stack of 3 sheets when the backs come out reversed.
- Fronts PDF: front 1, front 2, front 3.
- Backs PDF as scanned: back 3, back 2, back 1.
- Interleaved with Reverse the backs on: front 1, back 1, front 2, back 2, front 3, back 3.
Merge odd and even pages
Some people print or export a document as two files, one with the odd pages and one with the even pages. Add the odd pages PDF first and the even pages PDF second, then turn Reverse the backs off, since the even pages are already in order. The result is pages 1, 2, 3, 4 in sequence.
Front first is the default. Pick Back first when the second file holds page 1, for example when the odd and even files were swapped by mistake and you would rather not move them.
When the fronts and backs do not match
A missed sheet or a jam gives sets of different lengths. With Add the extra pages at the end, the tool pairs pages until the shorter set runs out, then places the rest in order. With Insert blank pages, each unpaired page gets a blank page of the same visible size next to it.
When the backs are reversed, they are reversed first and paired second. If a back is missing from the middle of the stack, every pair after it is off by one. The preview makes this easy to spot. Rescan the missing side, or drag the pages into place afterwards with the Delete / Reorder tool.
Blank backs and other cleanup
Interleave keeps every page. If some sheets were printed on one side only, their scanned backs come out as blank pages in the result. Remove them afterwards with Delete PDF Pages by tapping each blank thumbnail.
Scans often need more work after the pages are in order.
- Straighten crooked pages with Deskew Scanned PDF.
- Add a searchable text layer with OCR PDF.
- Shrink a file that is too big to email with Compress PDF.
- Turn sideways pages upright with Rotate PDF.
What the interleaved PDF keeps
Page content, page sizes, crop areas and rotation come across unchanged, and the file size is about the size of the inputs added together. Web links on the pages keep working.
Bookmarks from the source files are not carried over, because their page order no longer applies. Form fields may stop working, so fill in forms first or use Fill PDF Form before you interleave. The title and author fields start empty and you can set them with PDF Metadata.
A PDF that only blocks printing or copying opens as it is. A PDF that needs a password to open must go through Unlock PDF first.
Frequently asked questions
Add the fronts PDF first and the backs PDF second, set Reverse the backs to match how you scanned, and check the Page order preview. Then press Interleave pages and download the result.
Scan the fronts, turn the stack over and scan the backs. Add both files here with Reverse the backs on. The tool pairs the last scanned back with the first front, so every sheet ends up front then back.
Yes. Add the odd pages file first and the even pages file second, and turn Reverse the backs off. The pages come out as 1, 2, 3, 4 and so on.
Yes. Add only that file and enter how many of the first pages are fronts. The rest are treated as the backs.
Pages are paired until the backs run out. The remaining fronts either follow at the end, or each gets a blank page after it if you pick Insert blank pages.
Yes to both. It runs in any modern browser on Windows, Mac, Linux, iPhone, iPad and Android, with no account, watermark or software to install. Your scans are read on your device and never uploaded.
If page 2 of the result shows the back of the last sheet, the backs were scanned in order and Reverse the backs should be off. If the backs line up only near the middle, the reverse setting is right but a sheet is missing or doubled in one of the scans.
No. Pages are copied as they are, so images keep their resolution and any OCR text stays searchable.
