Same settings, many pages — memory is the real limiter
“Batch” means two jobs people confuse: (1) every page of one long manual, which Instant pdf-lib already does with a single configuration, and (2) dozens of separate PDFs, which needs Premium because a browser tab cannot reliably hold an enterprise folder. 100MB+ scanned books also need Premium for RAM headroom. Processing still happens locally in a Web Worker — Premium is not “now we upload to Convertify4u.” It is capacity. Group similar files; do not mix encrypted and open PDFs in one mental queue. Compress first only if size is the problem; stamping a 400-page scan is already heavy. Uniform CONFIDENTIAL across a legacy archive is the usual compliance story. Per-page unique text is not this workflow — split first if covers need a different line. Spot-check page 1 and the last page: some scans have a blank back sheet you do not want to discover after emailing 400 files.
Queue hygiene
Name outputs clearly (filename-stamped.pdf). Spot-check the first file at 100% before you grind through hundreds. Keep unmarked originals in a separate folder.
Free versus Premium
One ordinary PDF, all pages: free Instant. Multi-file stacks and oversized packs: Premium via Lemon Squeezy — stated before you start, not mid-download.