What does PDF mean, and why is everything sent as one?
A PDF is a page frozen in a file. Whoever made it chose the fonts, the margins and where every picture sits, and the PDF carries all of that along, so it looks the same on a phone, a Mac, a Windows laptop or a printer. That is the whole point of the format, and the reason forms, invoices, tickets, contracts and exam papers arrive as PDFs rather than Word files.
Adobe started it. Its co-founder John Warnock began the idea in 1991 as the Camelot Project, and by 1992 it had become PDF. It is now an open standard maintained by ISO (ISO 32000), which is why every browser, phone and operating system can open one without Adobe software.
The trade-off is that a PDF is built for reading, not changing. Text sits at fixed positions on the page instead of flowing like a Word document, so editing one means working with that layout rather than retyping a paragraph. Some PDFs hold no text at all: a scan is a photo of a page, and until text recognition (OCR) is run on it, you can’t search or copy a word of it.
How can you tell what kind of PDF you have?
Try to select a word. If the text highlights, the PDF has a real text layer: it can be searched, copied, edited and read aloud. If the whole page selects as one block, or nothing happens, it is a scan, a picture of a page inside a PDF.
That one test explains most PDF trouble. Scans are big, which is why a phone scan of three pages can be 15 MB while a 40-page report from Word is 400 KB. They can’t be searched until they go through OCR PDF. And “editing” a scan means covering the old words, because there are no letters underneath to change.
For the rest, open the file in Adobe Acrobat Reader and press Ctrl+D (Cmd+D on a Mac) for Document Properties: page size, which fonts are embedded and whether it has a password. Or drop it on PDF Size Checker, which reports the size, page count and password in your browser.
How do you open, make or change a PDF?
To open one, you need nothing extra: Chrome, Edge, Safari and Firefox all display PDFs, and so do the Files app on an iPhone and the Files or Drive app on Android.
To make one, use Save as or Export as PDF in Word, Google Docs or Pages, or Print and choose “Save as PDF” in any browser. To build one from scratch, Create PDF lets you write a document with headings, lists and pictures and save it as a PDF, and Images to PDF turns photos into one.
To change one, pick the tool for the job instead of converting back and forth to Word: Edit PDF for a line of text, Sign PDF for a signature, and Compress PDF when it is too big to send.