What is actually inside a PDF, why it breaks, and which fixes are real.
Tomasz builds and breaks document tooling for a living. He wrote most of the engine behind this site, which means the troubleshooting guides here come from someone who has read the specification rather than someone paraphrasing a forum post. He is the author of the site's standing refusal to offer password cracking.
At a glance
- Role
- File formats and troubleshooting
- Writes about
- The PDF specification, encryption, text extraction, file repair
- Working in this field since
- 2017
- Guides on this site
- 14
Guides by Tomasz Kowalczyk
Why PDF text does not reflow
It is not an oversight and it is not fixable. A PDF describes a printed page, and reflowing would break the only promise the format makes.
Searching inside a PDF
Search works on characters in the text layer. Everything that goes wrong with it comes from that sentence, including searching across a whole folder at once.
How to tell whether a PDF is scanned
It takes two seconds, it determines what you can do with the file, and it explains most of the things people think are broken.
What is actually inside a PDF
Not a document. A list of pages, each holding drawing instructions, plus an index saying where everything lives. Five minutes here explains a year of PDF problems.
The text layer
The single most useful distinction in the whole format. Either the file contains characters or it contains a photograph of characters, and everything follows from which.
PDF metadata
Title, author, the software that made it, and sometimes the path it was saved from. None of it is on any page, and nothing you do to the pages touches it.
Why handwriting recognition fails
On printed text, recognition is close to solved. On handwriting it produces plausible guesses, and a plausible guess attached to a mathematical answer is worse than no text at all.
Encryption and permissions
One is cryptography and it holds. The other is a request that any reader is free to ignore. Most PDF security advice treats them as one feature with a strength dial.
Redacting a PDF properly
A black rectangle drawn over text leaves the text entirely intact underneath. This has ended careers, repeatedly, and it takes ten seconds to check.
What a PDF reveals
Your account name, the software you use, when you made it and sometimes where on your disk it lived. None of it is on any page and all of it travels with the file.
Choosing a PDF password
There is no recovery. That single fact should drive the whole decision, and it usually drives it in the wrong direction.
When a PDF will not open
Four causes, in order of likelihood, with a test for each. Most of them are recoverable and one of them is not, and you can tell which in about a minute.
Why text will not copy
Three causes, and the first one accounts for most of them. All three are diagnosable in under a minute and only two have anything you can do about them.
When PDF pages are blank
Four causes, and they need four different responses. The one that matters most is the one where the pages are blank on paper but not on screen.