Compress multiple PDFs in one run
Batch compressing PDFs means shrinking many files in one run instead of feeding them through a compressor one at a time; this tool applies a single resolution and JPEG-quality setting to every file in your stack, processing them sequentially in your browser and reporting the combined before and after sizes. Nothing is uploaded, and each output keeps its original filename.
How it works
The compression method is the same rasterizing pipeline used by our single-file compressor: each page of each PDF is rendered by the pdf.js engine onto an off-screen canvas at the chosen resolution, the canvas bitmap is encoded as a JPEG at the chosen quality factor, and a new PDF is assembled with one full-page image per page at the original page dimensions. JPEG's discrete cosine transform discards high-frequency detail the eye barely registers at reading size, which is where the savings come from — and why scans and image-heavy files shrink dramatically while the outputs contain no live text.
What batching adds is orchestration. The files are queued and processed strictly one at a time, not in parallel. That choice is deliberate: rendering a page to canvas can briefly demand tens of megabytes, and running twenty files simultaneously would multiply that peak by twenty and crash the tab on ordinary hardware. Serial processing keeps peak memory near the requirement of the single largest file, so a stack of 40 scans finishes as reliably as one. Each file's canvases and buffers are released before the next file begins.
One setting governs the entire run — that uniformity is the point. When a folder of scanned receipts or course handouts all came off the same scanner at the same bloated resolution, choosing a setting once and letting the queue run beats repeating the same clicks forty times. As each file completes, its individual before and after sizes are recorded, and the run ends with a total: how many megabytes went in, how many came out. Files where compression would not help — rare, but possible with lean text-only PDFs whose pages cost more as images than as text — are still processed with the same setting, and their per-file numbers make any such regressions visible in the report.
Illustrative example: 23 expense receipts, 96 MB down to 9.8 MB
Illustrative scenario, not a recorded benchmark. File sizes, timings and results depend on the input and device. Try the reproducible samples.
An accountant's monthly expense folder holds 23 phone-scanned receipts and invoices totaling 96.4 MB — individually between 1.8 and 7.2 MB, all destined for an accounting system that becomes sluggish past 10 MB per upload batch.
All 23 files go into the tool in one drop, with quality set to 0.7. The queue runs for about 90 seconds on a mid-range laptop, ticking through each file in turn. The report at the end reads: 96.4 MB in, 9.8 MB out — an 89.8% overall reduction. The largest single file, a 7.2 MB five-page invoice, came down to 0.6 MB; the smallest, a one-page 1.8 MB parking receipt, to 110 KB. Every output kept its original filename, so the folder structure on disk needed no renaming before upload. Doing the same job through a single-file compressor would have meant 23 separate select-compress-download cycles for an identical result.
Batch compression — frequently asked questions
How can I compress many PDF files at the same time?
Select or drop all the files at once, pick one quality setting, and the tool works through the stack file by file, re-encoding every page. When the run finishes you download the compressed copies and see the total size saved across the batch.
Does every file in the batch get the same compression settings?
Yes, one resolution and quality setting applies to the whole run, which is what makes batching fast. If individual files need different treatment, or one must hit an exact limit, compress those separately with the single-file or target-size tool.
Are the files processed in parallel or one at a time?
Sequentially, one file at a time. Rendering pages to canvas is memory-hungry, and processing serially keeps peak memory near the size of the largest single file instead of the whole stack, so large batches finish reliably.
Will batch compression keep the text selectable in my PDFs?
No. Each page is re-encoded as a JPEG image, so the outputs contain pictures of pages rather than live text, fonts, or form fields. Keep the originals if you may need to search or copy text later.
Is there a limit on how many PDFs I can batch compress?
There is no fixed file-count cap because nothing is uploaded; the practical limit is your device's memory and patience. Batches of 20 to 50 typical scans are routine on an ordinary laptop.
Do my PDFs get uploaded when I compress them in bulk?
No. The whole pipeline, from rendering to JPEG encoding to rebuilding each PDF, runs in JavaScript in your browser tab. You can disconnect from the network after the page loads and the batch still completes.