PDF guides
Long-form explanations of how PDFs actually work — written to be useful whether or not you ever open our editor. No listicles, no affiliate links, and no claims we cannot back up.
What is actually inside a PDF file
A PDF is not a document in the way a Word file is — it is a set of drawing instructions. Here is what the format really contains, and why that explains almost every frustration you have had with it.
8 min read · Updated 12 August 2026
What happens when you upload a PDF to an online tool
Where your file actually goes when you drop it on a free PDF website, what "deleted after one hour" really covers, and how to check for yourself whether a tool uploads anything at all.
9 min read · Updated 12 August 2026
What PDF metadata reveals about you
Author names, software versions, timestamps, earlier revisions and text hidden under black boxes. What a PDF carries beyond its visible pages, and how to check before you send one.
8 min read · Updated 12 August 2026
Is a signature drawn on a PDF legally valid?
The difference between a drawn signature, a cryptographic signature and a qualified one — what eIDAS and the US ESIGN Act actually require, and which you need for which document.
9 min read · Updated 12 August 2026
Why PDF files get so large, and what actually shrinks them
Why a three-page document weighs 40 MB, what PDF compression really does, which settings matter, and why zipping a PDF saves nothing.
8 min read · Updated 12 August 2026
Scanned PDF vs text PDF: what OCR really does
Why you cannot select text in some PDFs, how optical character recognition builds an invisible text layer, what makes it accurate, and how to tell the two kinds of file apart in five seconds.
8 min read · Updated 12 August 2026
Why these exist
PDF is thirty years old, standardised as ISO 32000, and almost universally misunderstood — including by people who work with it every day. Most of what is written about it online is either a specification too dense to read or a thin page whose actual purpose is to rank for a keyword and sell you a converter.
These guides aim at the gap in between: enough technical detail to explain why a thing happens, written for someone who is not going to implement a PDF parser. Where the honest answer is "a server does this better than a browser", we say so, even though we are a browser-based tool.
Looking for a specific task?
The guides explain the how and why. If you just need to get something done, the tool pages are the shorter route: merge PDFs, split a PDF, sign a document, rotate pages, delete pages, convert to images, images to PDF, extract text, add a watermark or add page numbers.