How to reduce the file size of a scan
In order of how much they save, and with the one that everyone tries first listed last, because it is the least effective.
Guides
Articles on PDFs, past papers and revision
Working with PDFs, properly. 40 guides across eight topics, written by four named people and tested against real documents. No article here exists to occupy a search result.
Working with past exam papers as PDFsPast papers, mark schemes and the folder they live in.5 guides
How to revise effectively from PDFsTurning documents into revision you will actually do.5 guides
Reading PDFs on any deviceWhy PDFs read badly on screens, and how to fix it.5 guides
PDF basics: pages, fonts, text layers and metadataWhat is inside the file, and why it matters.5 guides
Printing PDFs properlyScaling, duplex, booklets and the fit-to-page trap.5 guides
How to scan handwriting for online submissionPhotographing paper so a marker can actually read it.5 guides
Keeping a PDF private: encryption, redaction and metadataEncryption, permissions, redaction and metadata.5 guides
Troubleshooting a PDF that misbehavesDiagnosing the file rather than guessing at it.5 guides
Guides, page 3
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.
Condensing a mark scheme
Extract it to text, delete everything you already know, and what remains is a revision document of exactly your gaps - written by the act of deleting.
Missing fonts: why a PDF changes on another machine
A PDF is supposed to look identical everywhere. When it does not, the cause is almost always a font that was never put inside the file.
Choosing a scan mode for handwritten notes
Black and white produces files a fraction of the size and erases faint pencil. Greyscale keeps everything and costs more space. The choice depends on what you wrote with.
Why a PDF is enormous
Almost always images. Working out which images, and whether anything can be done about them, takes two minutes and prevents a lot of pointless compressing.
Revision that works offline
Every session that depends on a network is a session a network can end. The fix takes twenty minutes once and removes an entire category of lost evening.
Vector or raster: how diagrams are stored in a PDF
One is a set of instructions and the other is a grid of pixels. Which one a diagram is determines whether you can extract it, how big the file is, and what compression will do.
How fit-to-page scaling spoils graph questions
It shrinks the page by a few per cent, which changes every measured length on it. The printout looks completely normal and every gradient you read off it is wrong.
Getting a revision pack printed right first time
Merging, numbering, and deciding what gets printed at full size and what gets printed four to a sheet. Ten minutes of preparation and a ream you do not waste.
When a PDF looks different elsewhere
The format exists to prevent exactly this. When it happens anyway there are three causes, and you can identify which in about a minute.
Choosing a PDF reader
For most documents, the one already on your device. The question is normally asked because a particular file is misbehaving, and the file is usually the problem.