Good to know
Why open a PDF here instead of uploading it?
Most “free online PDF” sites upload your document to their servers first. For a menu that is fine; for a passport scan, a payslip or a signed contract it is not. Here the file is read by your browser and never sent anywhere.
Under the hood this viewer uses PDF.js — the same open-source engine that powers the PDF viewer built into Firefox — so fonts, images and layouts render the way the author intended.
If a PDF shows up but you cannot select text, it was most likely made from scanned images. In that case there is no text layer to copy from; you would need OCR software to turn the pictures back into text.