Introduction to PDF Fonts

As a developer working with PDFs in applications, it’s important to have an understanding of how fonts can impact text rendering and formatting. This guide will provide you with a high-level introduction to the key concepts related to fonts in PDFs, empowering you to work effectively with PDF documents in your web application using our PDF SDK.

Rendering Fidelity

Text rendering fidelity refers to how accurately a PDF document’s textual content is displayed and printed in different PDF viewers or printers. Text rendering fidelity is primarily influenced by fonts.

In many cases, the font data is embedded inside the PDF, resulting in the highest degree of text rendering consistency across user devices, PDF viewers, and printers.

When the font isn’t embedded inside the PDF, the PDF viewer will attempt to find a similar font installed on the user’s system (a process called “font substitution”). The substituted font can vary between different PDF viewers and operating systems, leading to inconsistent rendering for different users. Examples of this include:

  • Layout and spacing — The substituted font may not match perfectly the original character spacing, size, and position. Text could be clipped, overlap with neighboring characters, or flow outside its designated boundaries, affecting readability and aesthetics.

  • Missing glyphs — If the substituted font lacks the required characters or glyphs, the PDF viewer may display placeholders, question marks, or empty boxes instead of the correct characters. This is particularly common when the user enters non-Latin script into PDF form fields or as text annotations, and the PDF is then opened by someone without the foreign language font.

  • Text clarity — The substituted font may not support font hinting and anti-aliasing, leading to less crisp and clear text rendering, especially at lower resolutions.

  • Loss of formatting — Font substitution can result in the loss of formatting, including bold, italic, and underlined text.

Types of Text inside PDF Documents

Within a PDF, you’ll encounter a variety of textual content where fonts impact how the text is rendered:

  • Regular text — This is the most common type of text in a PDF document. It includes body text, paragraphs, headings, titles, lists, hyperlinks, page numbers, and any textual content within the document.

  • Annotations and comments — These can include free text annotations and comments.

  • Form fields — Interactive PDF forms may contain various types of fields that can contain text that has been prefilled or input by the user.

  • Watermarks and stamps — Text-based watermarks or stamps are often used to mark the status of documents as confidential, draft, or approved, or to add copyright information.

  • Mathematical equations and symbols — Academic and scientific PDFs may feature mathematical equations, formulas, and special symbols, often rendered using specialized fonts or markup languages like LaTeX.

  • Digital signatures — Digital signatures in PDFs can include text elements to indicate the signer’s identity, date, and certification status.


A common issue is when the user inputs non-Latin text into a form field or text annotation, which then doesn’t render correctly when the PDF is opened in other PDF viewers. PSPDFKit’s dynamic font loading capability can solve this.

How PSPDFKit Handles Fonts

The PSPDFKit SDK sits on top of an optimized fork of PDFium, the same PDF engine used in Chromium, Android, and countless other applications. Here’s how PSPDFKit’s PDF viewer ensures a high degree of text rendering precision:

  • Font matching and substitution — Employs a font substitution mechanism to find a suitable alternative system font if a required font isn’t embedded in the PDF. Developers can also have granular control over font substitution, dynamic font loading, and custom fonts, or alternatively opt for the hands-off approach of our Web Server-Backed product.

  • Unicode support — Handles a wide range of characters and scripts from different languages. This ensures that text in various languages and writing systems is correctly rendered.

  • Font hinting and anti-aliasing — Optimized font hinting and anti-aliasing settings, allowing for precise and high-quality text rendering.

  • Cross-platform compatibility — As the world’s most popular PDF rendering engine, PDFium is designed for cross-platform use and aims to provide consistent rendering across various operating systems, including Windows, macOS, Linux, and Android. This ensures PDF documents display consistently, regardless of the user’s device or platform.

To learn more, read our guides on handling fonts: