No. Neither of your PDFs is uploaded when you use Alternate Mix PDF — both documents are loaded, combined, and saved entirely inside your browser tab, with nothing transferred to a Lizely server, no cloud copy made, and no remote processing involved at any point. The two files stay on your device from the moment you pick them until you download the finished, alternated PDF. This matters when you're working with scanned contracts, internal reports, marked exam papers, or private translations, and you need the merged output but don't want the source pages leaving your laptop. Teachers merging odd and even worksheets, accountants pairing back-up scans with stubs, and lawyers interleave front and back duplex scans are all common cases where the upload question is the first thing asked. Because everything happens locally, the same answer applies on every visit, on every operating system, and on every network: the page interleaving, the copy step, and the final download all execute inside the one tab where you opened the tool.
No Upload, No Cloud Copy — Where the Work Actually Happens
The privacy promise comes from how Alternate Mix PDF is built, not from a policy you have to trust. Page copying uses the pdf-lib library running directly in the tab you have open. That library takes PDF A and PDF B as binary objects in your browser's memory, copies pages from each source using the library's copyPages function, assembles them into a fresh PDF document, serializes that document once, and hands you a downloadable blob URL. At no stage is either source document sent over the network, attached to a request, or stored on a remote system. Replacing either input clears the previously generated output and revokes the stale download URL, so a slower earlier run cannot overwrite the result built from the newer files you just picked. The same local-only architecture appears across related Lizely tools; you can confirm the same approach on the no-upload flip tool.
What Alternate Mix PDF Does
Beyond privacy, Alternate Mix PDF has a single, narrow job: interleave the pages of two PDFs into a single downloadable file in a documented order. You pick a first input, which the tool labels as A, and a second input, labeled as B. The output sequence is fixed: page 1 of A, page 1 of B, page 2 of A, page 2 of B, and so on. When one document runs out first, every remaining page from the longer document is appended in its original order. So a three-page A combined with a two-page B produces A1, B1, A2, B2, A3, and a one-page A combined with a three-page B produces A1, B1, B2, B3.
Each copied page keeps its own page-box dimensions, rotation, vector drawing, text, and embedded raster content, to the extent the library's copy operation supports it. The tool does not force every output page to match the size of the first document, does not stretch content, does not rasterize text into bitmaps, and does not insert blank separator pages. The interface does not reverse a source, either; if a scanner saved pages in reverse order, you need to fix that with Reorder PDF Pages before mixing.
Run the Alternating Mix on Two Local Files
- Open Alternate Mix PDF in your browser. The two file pickers are labeled in order: the first selection becomes A and supplies the first output page, and the second becomes B.
- Pick PDF A. The file must be a non-empty PDF no larger than 25 MiB. The page count of A appears in the result preview as soon as the file loads.
- Pick PDF B. The file has the same 25 MiB limit and must also be a non-empty PDF. The page count of B appears in the result preview alongside A's count.
- Verify both source files are already in the intended internal order. If either one is reversed or scrambled, use a reorder tool first, because Alternate Mix PDF will not guess the correct order from filenames or page content.
- Click Alternate and mix PDFs. The tool copies pages in A1, B1, A2, B2 order, appends any leftover pages from whichever document is longer, and builds the new PDF inside the same tab.
- Read the result line carefully. It reports the page count of A, the page count of B, and the total page count of the output. The total must equal A + B; if it does not, do not download and re-pick the files.
- Download the new PDF. The filename combines the cleaned names of both sources and adds "-alternated.pdf". Your original two files remain unchanged on disk.
How the Output Pages Line Up
The interleaving rule is deliberately fixed so you can predict the final sequence before downloading. The table below shows what comes out for common combinations of A and B, using only the document totals that the result line reports for you. The exact totals come from the tool's output page count for the chosen inputs.
| A pages | B pages | Output sequence | Output total |
|---|---|---|---|
| 3 | 2 | A1, B1, A2, B2, A3 | 5 |
| 1 | 3 | A1, B1, B2, B3 | 4 |
| 4 | 4 | A1, B1, A2, B2, A3, B3, A4, B4 | 8 |
| 2 | 5 | A1, B1, A2, B2, B3, B4, B5 | 7 |
The pattern is simple to remember. Walk through both documents page by page. At each step, take the next page from A, then the next page from B, until one document is exhausted. Whatever pages remain in the longer document are appended at the end in their existing order. Swapping the two selections under their original names (so B is picked first) flips the lead: B1, A1, B2, A2, then the leftover tail from whichever document is now longer.
When to Pick Alternate Mix PDF Over Another Tool
The interleaving job is unusual enough that it is worth checking you have the right tool for what you actually want. The table below compares Alternate Mix PDF with the closest neighbors in the same tool family so the right choice is easy to make.
| Tool | What it does to your pages | Pick it when |
|---|---|---|
| Alternate Mix PDF | Copies A1, B1, A2, B2, then appends tail pages from the longer document | You need front and back scans interleaved, question/answer sheets paired, original and translated pages alternated, or odd/even batches joined in order |
| Merge PDF | Appends all pages of A, then all pages of B, in your chosen file order | You just want a single combined document in a flat A-then-B sequence |
| Reorder PDF Pages | Lets you drag pages of a single PDF into a new order | One source is reversed, scrambled, or has pages in the wrong place |
| Booklet PDF | Imposes pages into a two-up, printable folded booklet layout | You need to print a saddle-stitched booklet, not an alternated reading sequence |
If the desired truth is the documented A/B alternating sequence with unmatched tail pages preserved, Alternate Mix PDF is the correct choice. If you actually need a flat A-then-B concatenation, Merge PDF is faster and simpler.
Limits, Errors, and Memory to Plan For
A few practical limits are worth knowing before you start, because they change whether the tool can finish the job without surprises.
- Per-input size cap: each PDF must be non-empty and no larger than 25 MiB. The 25 MiB limit applies to A and to B separately, not to their combined output size.
- File condition: encrypted, password-protected, damaged, oversized, or incorrectly labeled files produce a visible error. Password protection is not bypassed, so remove the password first with Remove PDF Password if you already know it.
- Memory cost: because the operation runs in one browser tab, both source documents and the newly serialized result may coexist temporarily in memory. On a memory-constrained device, close other heavy tabs before mixing, and keep irreplaceable originals outside the browser workflow as a backup.
- Interactive features: form fields, bookmarks, outline destinations, scripts, attachments, and cross-document links may not survive page copying with the same semantics. The tool does not promise preservation of those advanced structures, so inspect any interactive PDF after mixing.
- Stale output: if you replace one input after producing a result, the old output is cleared and the previous download URL is revoked, so a slower earlier job cannot replace a result made from newer files.