Search for a PDF tool and almost every result works the same way: your file travels to a server, the server does the work, and a sentence promises deletion within the hour. For a public brochure that is fine. For a signed contract, a payslip, a medical letter or an invoice with bank details, it means a company you know nothing about holds a copy.
These tools run the whole operation in your browser. There is no size limit beyond your own memory, no queue, and nothing to delete afterwards. If you know how to open your browser’s developer tools, you can watch the proof yourself: no request ever carries your file.
Questions
Is there a file size limit?
Only your device memory. There is no server, so no upload limit and no queue. Very large scans may be slow on an older phone.
Are password-protected PDFs supported?
Only if they are not truly encrypted. A PDF with an owner password can usually still be read; one that needs a password to open cannot.
Does quality suffer?
No. Pages are copied rather than re-rendered, so there is no re-compression and no loss.