Add support for a strikethrough property or strikethrough-related properties in the TextProperties class.

Add support for creating Tables and applying tables styles (predefined ones or custom).

Handle import of documents with wrong type of action key.

Once this is completed use the Exceptions Handling mechanism to handle this scenario. For instance:

private void ImportSettings_DocumentUnhandledException(object sender, DocumentUnhandledExceptionEventArgs e)
{
    if (e.Exception is InvalidActionException)
    {
        

Matte color is used for preblending images with some background color, using the SMask. Matte color is specified using the optional 'Matte' entry for the SMask object.

See PDF 1.7 specification, page 554-555:

Matte
array
(Optional; PDF 1.4) An array of component values specifying the matte color with which the image data in the parent image has been preblended. The array consists of nnumbers, where n is the number of components in the color space specified by the ColorSpace entry in the parent image’s image dictionary; the numbers must be valid color components in that color space. If this entry is absent, the image data is not preblended.

This allows specifying a soft mask in the external graphics state.

SkiaImageFormatProvider: Add support for Text, TextMarkup, Line, and Stamp annotations.

Currently, these annotations are omitted on image export.

At this point, the justify alignment is not supported. Provide the ability to export text with this setting.
This functionality is dependent on PdfProcessing: Provide API for setting the text alignment to Justify

Add support for "Invert if negative" property of chart data series fill.

More information about the feature can be found here: https://support.microsoft.com/en-us/office/add-or-remove-line-numbers-b67cd35e-422c-42eb-adc9-256ca9802e22

In Excel this can be achieved by right click on the axis, then from the context menu select "Format Axis".  Go to the "Text Options" tab and "Text Box" group and then in the "Custom angle" field insert the desired value.