In addition to the fast document generation, the SpreadStreamProcessing can be adapted to import documents significantly faster than SpreadProcessing.

Such fonts are:

• ArialMT - should fallback to Arial
• TimesNewRomanPS-ItalicMT, TimesNewRomanPS-BoldMT, TimesNewRomanPS-BoldItalicMT - should fallback to the Times New Roman variants accordingly. 

Currently, for .NET Framework scenarios, this could be achieved using RadPdfViewer's WPF control ThumbnailFactory class. Sample code may be seen at this forum post:
http://www.telerik.com/forums/pdf-thumbnail-returns-transparent-images#jO33X-E8Cki_qLh_KsToWg.
The feature should be implemented for .NET Standard as well.

If a worksheet spans more than one page, you can print row and column headings or labels (also called print titles) on every page to ensure that the data is properly labeled.

Office Open XML defines a mechanism for the storage of content which is not defined by this Office Open XML Standard, for example extensions developed by future software applications.

The stored data could be an image.

The attached sample project below demonstrates a possible workaround for PAGE and NUMPAGES fields when exporting to PDF. The demo shows how to generate document from scratch containing PAGE and NUMPAGES fields and export it to PDF.

Hidden fields with pushButton widget become visible when using FlattenFormFields method to flatten fields.

Workaround: do not flatten fields if the IsHidden property of any of its Widget's is set to True:

 var fieldsList = formFields.ToList();
 for (int i = 0; i < fieldsList.Count; i++)
 {
     var field = fieldsList[i];
     bool flattenCurrentField = true;
     if (field.FieldType == FormFieldType.PushButton)
     {
         PushButtonField pushButtonField = (PushButtonField)field;
         PushButtonWidget[] widgets = pushButtonField.Widgets.ToArray();

         foreach (var widget in widgets)
         {
             var baseType = typeof(PushButtonWidget).BaseType.BaseType.BaseType;
             PropertyInfo[] properties = baseType.GetProperties(BindingFlags.NonPublic | BindingFlags.Instance);
             PropertyInfo isHidden = properties.FirstOrDefault(p => p.Name == "IsHidden");
             bool value = (bool)isHidden.GetValue(widget);
             if (value == true)
             {
                 flattenCurrentField = false;
                 break;
             }
         }
     }

     if (flattenCurrentField)
     {
         document.AcroForm.FlattenFormField(field);
     }
 }