The JournalUpdated 17 October 2026
Read it while the
file is still open.
Short guides on the decisions behind PDFs, images, spreadsheets and privacy. Every one of them ends somewhere you can actually do the job.
Each guide takes one job people do with files, such as getting a PDF under an upload limit, opening a CSV in Excel without losing leading zeros, or working out what a JWT actually proves, and explains the decision behind it: what the format does, where the usual method goes wrong, and what to check afterwards. Every guide is written for this site and ends at a tool here that does the job in your browser, so you can try the advice on your own file straight away. When a guide is corrected, the page shows the date it was updated next to the date it was first published.
72 guides5 subjects
Sending a spreadsheet to someone who does not have Excel
The right format depends on one question: does the other person need to read the numbers, reuse them, or change them? Each answer has a different file.
Ends at Excel to PDF, Excel to CSV, CSV to Excel
Opening a PSD or AI file when you do not have Adobe software
Designers send working files because that is what they have open. You only need the picture. Both Photoshop and Illustrator files usually carry a ready-made copy of it.
Camera RAW files, and the JPG hidden inside every one
A RAW file is not a photo. It is the sensor's measurements, waiting to be developed. But every camera also tucks a finished JPG inside, and that is often all you need.
Taking pages out of a PDF: split, delete, extract, and which you want
Three buttons that look like the same operation. The difference is how many files come out and what happens to everything you did not select.
Page numbers, headers and margins: making a PDF look submitted, not exported
A PDF page has four different boundaries and a rotation value that does not move any content. Both explain why stamped text lands in odd places.
Making a PDF out of HTML, plain text and a form you filled in
A web page has no pages. Turning one into a PDF means inventing page breaks, and where they land is the whole problem.
iPhone photos in HEIC: opening, sharing and converting them
You send a photo from your iPhone and the other person gets a file they cannot open. The photo is fine. The format is the problem, and it has three fixes.
Making a GIF that is not 40 megabytes
A five-second clip becomes a 40 MB GIF and a 900 KB MP4 of identical quality. GIF is not a video format, and that is the whole explanation.
Reading text off an image: what OCR gets right and where it fails
The difference between 99% and 80% accuracy is usually the photo, not the engine. Most of the fix happens before any text is recognised.
MIME types, magic bytes and why a file opens as the wrong thing
An upload rejects your PNG for not being a PNG. The extension says one thing, the first eight bytes say another, and the server believes the bytes.
What a user agent string actually says about you
Every browser claims to be Mozilla. The string is part identification, part historical fiction, and it is a weaker signal every year.
QR codes: what is actually encoded, and how to make one that scans
There is no database behind a QR code. Everything it knows is printed in the squares, which is why a long URL makes a code nobody can scan.
Merging CSV files whose columns do not line up
Twelve monthly exports, one combined file. Two of the months added a column, one renamed another, and a naive concatenation hides all of it.
Unit conversion is not one multiplication
Twice the temperature in Celsius is not twice the temperature. Half the conversions people treat as multiplication are not multiplication.
Why zipping your photos saves nothing, and what to do instead
Zipping a folder of holiday photos and watching it shrink by 0.4% is not a broken tool. It is the correct answer to the wrong question.
Signing a PDF: what a signature image proves, and what it does not
Most documents people call "signed" contain a JPEG of a name. That is often fine, and it is worth knowing exactly what it is, because it proves almost nothing on its own.
Generating a random string that is actually random
Two generators produce strings that look equally random. One of them lets an attacker predict every future value after seeing a few.
What actually makes a password strong (it is not the special characters)
P@ssw0rd! satisfies every complexity rule ever written and is one of the first things any cracking tool tries. Here is what the maths actually says.