A scanner that only reads one side of a sheet leaves you with two files: every front page in one, every back page in the other. Neither is much use alone, and pasting them together end to end puts all the fronts before all the backs. Alternate Pages deals the two files together a page at a time, so the first front is followed by the first back, then the second front, and so on. Because a stack of sheets comes out of the feeder the other way round when you turn it over, there is a switch to read the second file from its last page instead of its first.
How to use Alternate Pages
- Add the file with the odd-numbered pages first, then the file with the even ones. The list shows the order they will be read in, and you can drag the rows to change it.
- If the second file was scanned back to front, which is what happens when you flip the whole stack and feed it again, turn on reversing the second file.
- Leave the pages-at-a-time setting at 1 for ordinary double-sided sheets. Raise it when each turn should take two or more pages, as with a booklet scanned two pages to a sheet.
- Select Alternate Pages and wait for the result.
- Open the download and check the first four pages. If a front is followed by the wrong back, the reversing switch is the setting to change.
How the pages are dealt
- One from each, in turn: The first page of the first file is followed by the first page of the second, then the second page of the first, and so on. It is the same motion as riffling two halves of a deck of cards together.
- The order of the list matters: Files are read top to bottom, so whichever you add first supplies the odd-numbered pages of the result. Drag a row up or down before processing to change which file leads.
- Uneven files still work: When one file runs out, the remaining pages of the longer one are added to the end in their original order rather than being dropped.
- More than two files: A third and fourth file join the same rotation, taking a turn each time round. That suits a document split across several scanning passes.
Scanning both sides on a one-sided scanner
This is the situation the tool exists for, and it is worth knowing exactly what the feeder does to the order.
- Why the backs come out reversed: You scan the stack face down to get the fronts, then lift the whole stack, turn it over and feed it again. The sheet that was on top is now on the bottom, so the backs arrive in the opposite order to the fronts.
- What the reversing switch does: It reads the second file from its last page towards its first, which cancels the flip out. Turn it on whenever you flipped the stack as a block; leave it off if you fed the backs one at a time in the same order.
- Checking it worked: Look at pages one and two of the result. Page two should be the reverse of page one, not the reverse of the last sheet. If it is the last sheet, flip the switch and run it again.
What the result keeps and what it loses
- Pages are copied whole: Each page is carried across as it was, with its text, images, size and rotation untouched. Nothing is re-encoded, so a scan loses no quality.
- Bookmarks and form fields: Outlines and interactive fields from the original files are not carried into the mixed document. Add bookmarks afterwards if the result needs them.
- File names: The download is named after the first file you added, with a word appended, so it is easy to tell apart from the two you started with.
When people use Alternate Pages
Double-sided contracts on a simplex scanner
Scan the signed stack face down, flip it, scan again, then alternate the two files with reversing turned on. The result reads the way the paper does.
Two halves of a long scanning session
A feeder that jams halfway leaves two files that interleave rather than follow one another. Alternating them puts the document back into reading order.
Translations beside an original
Give a reader each source page followed by its translated counterpart, instead of making them jump between two documents.
Limitations to know
Both files are uploaded together and count towards the same size limit for a single request. Pages are copied without being re-encoded, so the result is roughly the size of the two inputs added together. Bookmarks, form fields and attachments from the source files are not carried over.
Alternate Pages: common questions
Which file should I add first?
The one holding the first page of the finished document, which for a double-sided scan is the fronts. Files are read top to bottom, so the first one supplies pages one, three, five and so on. If you add them the wrong way round, drag the rows to swap them before processing rather than starting again.
When do I need to reverse the second file?
Whenever you scanned the fronts, then turned the whole stack over and scanned again. Feeding a flipped stack reverses it, so the backs arrive last sheet first. Reversing the second file cancels that out. If you scanned the backs one sheet at a time in the same order as the fronts, leave it off.
What happens if one file has more pages than the other?
The extra pages are added to the end of the result in their original order. Nothing is dropped. This is normal when the last sheet of a stack is single-sided, and it is also a useful sign that a page failed to feed if the difference is larger than one.
Can I alternate more than two files?
Yes. Every file you add joins the rotation and takes one turn each time round, in the order they appear in the list. With three files the result runs first page of one, first of two, first of three, second of one, and so on.
Does this change the pages themselves?
No. Each page is copied across whole, keeping its text, images, dimensions and rotation exactly as they were. Nothing is compressed or redrawn, so scans do not lose quality and text stays selectable.