What is a PDF?
A PDF is a file that keeps its exact layout on any device, which makes it the standard for documents you send, print or sign.
Why it looks the same everywhere
A PDF stores text, fonts and images at fixed positions on a fixed page. A Word document reflows depending on your fonts and screen. A PDF doesn't, so a contract looks the same on your phone and on your bank's printer.
Text PDFs and scanned PDFs
Some PDFs hold real text you can select. Others are photos of pages. They look alike, but you can only search and copy from the first kind.
Why PDFs are hard to edit
Fixed positions mean there's no flow of text to edit. That's why most tools here work on whole pages, such as joining, cutting, turning and converting, or add something new on top, like text, a signature or a watermark. Changing text that's already in a PDF isn't something we offer.