I can reply regarding the big PDF file size.
The main difference in the file size comes from embedding of the true type fonts.
In your attachment, the other two PDF files (one created by MS Word and another by Aspose.Pdf) both do not have true type fonts embedded in them.
But Aspose.Words for .NET 6.0 always embeds subsets of true type fonts used by characters in the document.
For documents that consist entirely of US ASCII characters (32-127) it is possible not to embed true type fonts and MS Word seems to do just that (if you use characters outside of this range, it will start embedding true type fonts).
We have a similar option in Aspose.Words and I’ve made it public and it will be available in 6.0.1 in a few days. By default (I think we will leave it as it is), Aspose.Words will always embed true type font subsets.
/// True to embed true type fonts for ASCII characters 32-127.
/// Fonts for character codes greater than 127 are always embedded.
/// Default is true.
public bool IsEmbedTrueTypeFontsForAsciiChars
When I set this option to false, the document size comes down from 200kb to about 50kb. It is still a bit more than 20-30kb generated by MS Word and Aspose.Pdf.
The remaining difference is due to the fact we use lossless FlateDecode filter for image compression by default and we have not yet provided a public API to select a different compression. MS Word and Aspose.Pdf both seem to use JPEG compression in this case.
Also, the images are scaled down to 38% in the document and MS Word and Aspose.Pdf do resample (scale the image down) before outputting to PDF, whreas Aspose.Words outputs all the original image pixels. Although this might result in a bigger PDF size, it usually also results in better quality. Anyway, we plan to add an option to specify resampling of images during PDF export in Aspose.Words.