Why processing in the browser beats uploading
Most free PDF services work the same way. You upload a document, a server somewhere does the work, and you download the result. That model puts a copy of your file, whether it is a draft contract, a payslip, a passport scan or a medical report, on hardware you do not control, under a retention policy you have not read. PDFteka sidesteps the problem by never sending the file anywhere. Modern browsers can already read, rewrite and save PDF files on their own, so the entire job happens on the machine in front of you.
The practical benefits show up immediately. There is no upload wait and no download wait, so a 200-page report is handled at the speed of your processor rather than the speed of your connection. There are no queues at peak hours and no daily caps, because there is no shared server to ration. And there is nothing to delete afterwards: since the file was never copied off your device, the usual promise to remove your documents within an hour is simply unnecessary here.
The trade-off is worth stating plainly. Because the work happens locally, very large documents depend on your device's memory rather than on a data center, and an older phone will chew through a 500-page scan more slowly than a desktop will. In exchange, the file, its metadata and the record of what you did with it stay entirely with you.