PDF glossary
The terms you meet in Document Properties, preflight reports and the Issues pane, each with what it means for editing the text.
The words in this glossary are the ones you meet in Document Properties, in a preflight report, in an error message or in the Issues pane of PDF Textfix: embedded subset, CID font, ToUnicode, content stream, incremental update, certified PDF. Each entry gives the definition in one sentence, says where you are likely to see the term, and explains what it means when you want to change a line of text: whether the line can be edited, whether the font can draw what you type, and what saving does to the file.
The entries are grouped by what they describe: fonts, text, the structure of the file, kinds of document, and the terms of the app itself. Definitions follow the PDF specification and the documentation of the formats they name; where a term means something specific in PDF Textfix, such as a line edit or a fallback font, the entry says how the app uses it.
Fonts
7 terms
- CID font (CIDFont+F1)
- A CID font is a PDF font whose characters are picked by number from a large set through a map called a CMap; CIDFont+F1 is a generic name some PDF producers give such a font instead of its typeface name.
- Embedded font
- An embedded font is a font program stored inside the PDF file, so every viewer draws the text with the same character shapes instead of looking for the font on the reader's computer.
- Embedded subset font
- An embedded subset is an embedded font that holds only the characters the document uses, named with a tag of six capital letters and a plus sign, such as AAAAAC+IBMPlexSerif-Regular.
- Font embedding permissions
- Font embedding permissions are the flags a font's maker sets in the fsType field of the font's OS/2 table, saying whether the font may be embedded in a document and whether that document may then be edited.
- Font encoding
- A font's encoding in a PDF is the rule that turns each character code in a page's text into a shape of that font, through a standard table, a table with differences, or the font's own numbering.
- Glyph
- A glyph is one shape stored in a font, such as a drawing of the letter a or of the fi ligature, while a character is the unit of meaning that a shape stands for.
- Type 3 font
- A Type 3 font is a PDF font whose characters are drawn by small PDF drawing procedures stored in the file, instead of by a font program of outlines, so any shape, a bitmap included, can be a character.
Text
2 terms
- Outlined or rasterized text
- Outlined text is lettering converted into vector shapes with no font behind it; rasterized text is lettering converted into the pixels of an image. Both look like text, but the file holds no characters for them.
- ToUnicode map
- A ToUnicode map is a table in a PDF font that tells a viewer which Unicode character each character code stands for, so the text can be copied, searched and read aloud.
The structure of the file
9 terms
- Content stream
- A content stream is a stream object that holds a page's drawing instructions, for its text, lines and images, which a viewer carries out in order; it is usually stored compressed.
- Form field
- A form field is an interactive part of a PDF whose value is stored in the field itself, not in the text of the page, and drawn on the page by a widget annotation that viewers can redraw from that value.
- Incremental update
- An incremental update saves a PDF by appending the changed objects, a new cross-reference section and a new trailer after the original bytes, so the earlier version stays complete inside the file.
- Linearized PDF
- A linearized PDF is a file whose objects are ordered, with hint tables, so that a viewer reading it over a network can show the first page before the whole file has arrived.
- Optional content group (layer)
- An optional content group, which most apps call a layer, is a named set of page content that a PDF viewer can show or hide; the file says which groups are on when it opens.
- Outline (bookmarks)
- The outline is a PDF's own table of contents: a tree of titled items, often called bookmarks, each of which jumps to a place in the document.
- PDF version
- A PDF's version is the number in its first line, such as %PDF-1.7, naming the edition of the PDF specification the file follows; since PDF 1.4 the document catalog can raise it with a Version entry.
- Tagged PDF
- A tagged PDF carries a structure tree that gives its content a reading order and roles, such as heading or paragraph, for screen readers and text extraction; ActualText is the replacement text a tag or a marked span gives for what the page draws.
- Text object
- A text object is the part of a PDF content stream between the operators BT and ET, where the font is chosen, the text is positioned and its strings are drawn.
Kinds of document
4 terms
- Certified PDF
- A certified PDF is a PDF its author signed with a certification signature that also states which later changes are allowed: none, form filling and signing, or those plus comments.
- Digital signature
- A PDF digital signature is a digest of the file's bytes, all but a gap that holds the signature itself, signed with the signer's private key and stored with the certificate that names the signer; a change to any signed byte makes it fail to verify.
- PDF/A (archival PDF)
- PDF/A is the family of ISO 19005 profiles for keeping PDFs readable over decades: a PDF that leaves out whatever could change how it looks later and states in its metadata which part and level it meets.
- Permissions password
- A permissions password, which the PDF standard calls the owner password, records what readers of a PDF may do, such as print, copy or change it, without being needed to open the file.
Terms of the app
2 terms
- Fallback font
- In PDF Textfix, a fallback font is the font that draws a character you type when the line's own font cannot, chosen in a fixed order and marked in orange while you edit, or underlined when it comes from another copy of the line's own font.
- Line edit
- A line edit is one edited line of one document, the unit PDF Textfix counts once when a save writes that line without the watermark, however often the open file is saved.
Where do you see these terms on a Mac?
In four places, mostly. Acrobat’s Document Properties has a Fonts tab that lists each font of the file and whether it is embedded. The pdffonts command of Poppler, installed with Homebrew (brew install poppler), prints the same list with its emb, sub and uni columns. A preflight or validation report names the standard a file claims, such as PDF/A. And the Issues pane of PDF Textfix (⌥⌘I) names the lines it keeps read-only and the characters it drew from a fallback font.
Which entries explain a locked line?
A line PDF Textfix keeps read-only has a lock beside it, and the lock’s tooltip gives the reason. Each reason has an entry here: a Type 3 font, invisible text, a form field, an encrypted file or one whose permissions forbid changes, a certified PDF. A character drawn in orange points to the fallback font entry, and a file that grows with every save in another app points to the incremental update.
How the entries are written
Each entry opens with a one-sentence definition, then says where you meet the term: Acrobat’s Document Properties, the font list that pdffonts prints, a preflight report, or the Issues pane of PDF Textfix. It goes on to what the term means when you change a line of text, and what you can do about it.
Definitions follow ISO 32000, the PDF standard, and the documentation of the formats and tools they name. Each entry lists its sources with the day they were read, and links the guides that explain the term at length. Where an entry prints the output of a command, it comes from a demo document made for PDF Textfix or from a test file the entry describes, with the day it was made.