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Warning

Starting with version 26.9, GroupDocs.Signature for .NET no longer ships a .NET Standard build. On Linux and macOS use the .NET 6, .NET 8 or .NET 10 build; see System Requirements.

The .NET 6, .NET 8 and .NET 10 builds use System.Drawing for some image operations, for example image, stamp, barcode and QR-code signatures. On Linux and macOS this needs libgdiplus (see the recommendations below) and the System.Drawing.EnableUnixSupport switch in your application project:

<ItemGroup>
  <RuntimeHostConfigurationOption Include="System.Drawing.EnableUnixSupport" Value="true" />
</ItemGroup>

Without them, these operations throw GroupDocsSignatureException with the message “The type initializer for ‘Gdip’ threw an exception”. Install the fonts your documents and signatures use as well: a font that is not installed can also stop signing, with a “Font … was not found” message.

Fonts that a document uses but that are not installed on the machine are substituted with available fonts. This can change the layout when a document is rendered to PNG, JPG or PDF, so install the fonts your documents use.

When using GroupDocs.Signature in a non-Windows environment in order to improve rendering results we do recommend installing the following packages:

1. libgdiplus - is the Mono library that provides a GDI+-compatible API on non-Windows operating systems.
2. libc6-dev - package contains the symlinks, headers, and object files needed to compile and link programs which use the standard C library.
3. ttf-mscorefonts-installer - package with Microsoft compatible fonts.

To install packages on Debian-based Linux distributions use apt-get utility:

1. sudo apt-get install libgdiplus
2. sudo apt-get install libc6-dev
3. sudo apt-get install ttf-mscorefonts-installer