Text layer
Definition
The machine-readable text stored inside a document alongside its visual appearance. It is what makes search and text selection possible, and it is exactly what a scanned page does not have.
A born-digital PDF carries both a drawing of each glyph and a record of which character that glyph represents. Search works because the second thing exists. A scanned page carries only the picture — visually identical, functionally inert.
This is the single most common source of confusion in document search projects. "Search does not work on these files" almost always means "these files were scanned", and no amount of tuning the search engine changes that. The fix is OCR, which is a different and considerably more expensive operation.
Office formats are the easy case: a DOCX or an XLSX is structured text by construction, so the text layer is never in question.
In Doconut
Full-text search runs against the text layer and is provided by the paid AdvancedSearch plugin. If a document has no text layer, it renders correctly but returns no search hits.
Related terms
OCR (optical character recognition)
Reconstructing machine-readable text from an image of a page — the operation that gives a scanned document the text layer it was never born with.
Server-side document rendering
Converting a document into page images on the server, so the browser displays rendered pages rather than parsing the original file itself.
Document conversion
Transforming a file from one format into another and producing a new file, as distinct from rendering, which produces a temporary visual representation and no new artifact.