Fonts that are not embedded

A document can use a font without embedding it: the standard fonts, such as Helvetica, and fonts the author expected the reader to have, such as Arial or a corporate font. The renderer replaces each of them, in this order, by:

1. the font PdfRenderOptions.FontResolver returns for it;
2. for a standard font (Helvetica, Times, Courier and their aliases, such as Arial), the bundled Liberation font of its kind and style, whose glyphs have the same widths, so the text keeps its layout;
3. a font of the system that matches its name, weight and style, then one of its kind (serif, sans serif, fixed pitch), unless PdfRenderOptions.UseSystemFonts is false;
4. the bundled Liberation font of its kind.

The bundled fonts have the characters of the Latin encodings of PDF. Symbol and ZapfDingbats are only replaced by the resolver or by the fonts of the system.

The document gives the width of each glyph, which places the next one. A glyph of the replacement font is scaled horizontally to that width, so that the glyphs of a wider or narrower font neither overlap nor leave gaps (the text of vertical writing is not scaled).

Give the fonts of the application

// A font of the application, loaded once
var corporateSans = FontLoader.Load(fontData, new PooledFontEnvironment(FontResourceLimits.Default, maxLiveAllocationBytes: 64 * 1024 * 1024))[0];

var options = new PdfRenderOptions
{
    // Called for each font a document does not embed; null lets the library choose
    FontResolver = request => request.Name.StartsWith("Corporate", StringComparison.Ordinal) ? corporateSans : null,
    UseSystemFonts = false,
};

var document = PdfDocument.Open(file);
using var image = document.Pages[0].Render(options);

• The resolver is called for each font the document does not embed, the standard fonts included, with a PdfFontRequest: its Name (the PostScript name, without the tag of a subset), StandardName (the standard font it is or is an alias of, such as Helvetica-Bold for Arial,Bold), IsBold, IsItalic, IsSerif, IsFixedPitch and IsSymbolic.
• It returns a FontFace of Meziantou.Framework.Fonts, or null to let the renderer choose. Load the faces once, and share them between renderings.

Render the same pixels everywhere

With UseSystemFonts set to false, the fonts of the machine are never used: a page renders the same pixels on a developer machine, a server and a container, whatever fonts they have installed. Set it for thumbnails that are compared in tests, cached, or generated on several machines. The documents that embed their fonts do not depend on it.