BASALT · JOURNAL
Making a PDF readable by a screen reader
An accessible PDF is one a screen reader can present in a sensible order with the structure intact. Most PDFs are not, and scanned ones are not readable at all.
Why scans fail completely
A scanned page holds no text, so a screen reader has nothing to read. The page is silent.
OCR is the minimum fix and it is a large improvement: it produces text a screen reader can speak. It does not produce structure, so the result is readable rather than navigable.
What structure adds
A tagged PDF records that a piece of text is a heading, a paragraph, a list item, a table cell, or a figure with a description. That lets a reader navigate by heading, understand a table as a table, and skip what they do not need.
Without tags, a screen reader reads whatever order the content stream happens to be in, which for a multi column layout is frequently wrong: it reads across columns rather than down them.
The minimum worth doing
Make sure there is real text, by OCRing anything scanned.
Set the document language, so the reader pronounces it correctly.
Give the document a title in its metadata, because that is what is announced when it opens.
Ensure a sensible reading order, which for single column text usually follows naturally and for anything else needs checking.
Add alternative text to images that convey information. A decorative rule needs none; a chart carrying the argument of the page needs a description.
Where this gets specialist
Full compliance with accessibility standards is genuine work and there is a profession that does it. Complex tables, forms and mathematical content all need care beyond what a general PDF tool offers.
If you have a legal obligation to meet a standard, that is a specialist job. If you are simply trying not to publish documents nobody can read, the list above covers most of the distance.
The thing most people can fix today
Publishing scans with no text layer. It is the single largest accessibility failure in ordinary document publishing, it makes the document useless to a screen reader and unsearchable for everyone, and OCR fixes both at once.
Frequently asked questions
Why can a screen reader not read my PDF?
If it is a scan, the page contains a picture of text and no text at all, so there is nothing to read. OCR adds a text layer and is the minimum fix.
What is a tagged PDF?
One that records structure: which text is a heading, a paragraph, a list item or a table cell. Tags let a screen reader navigate by heading and interpret tables, rather than reading the raw content order.
What is the minimum for PDF accessibility?
Real text rather than a scan, a document language set, a title in the metadata, a sensible reading order, and alternative text on images that convey information.
Do I need specialist help for accessible PDFs?
For full compliance with a standard, yes, particularly for complex tables, forms and mathematics. For simply not publishing documents nobody can read, OCR and the basics cover most of the distance.
Doing it in Basalt
Basalt is a native macOS PDF toolkit: eighteen tools in one window covering merge, split, page organisation, compression, OCR, passwords, Bates numbering, forms, signing, watermarks and comparison. Every file is processed on your Mac, and the engine that opens documents holds no network entitlement at all, which macOS enforces at the code-signature level. Redaction destroys content rather than covering it, and an independent verifier proves the material is gone before a file is written. A one time $29 licence covers up to three Macs, free for the first 24 hours. basaltformac.com, or brew install --cask chipmunk1101/tap/basalt.
Redaction that proves itself
Basalt destroys the content you mark, then re-opens the file it wrote and proves the content is gone before it saves anything. Your documents never leave your Mac.