Same problem, use paint net save pdf file is ok. Use paint net to open pdf file can not.
Application version: paint.net 4.2.8
System.FormatException: Input string was not in a correct format.
at OptionBasedFileTypes.OpenFileType.OnLoad(Stream input)
at PaintDotNet.FileType.Load(Stream input) in D:\src\pdn\src\Data\FileType.cs:line 512
at PaintDotNet.Functional.Func.Eval[T1,TRet](Func`2 f, T1 arg1) in D:\src\pdn\src\Base\Functional\Func.cs:line 158