XnView Software

No, I find out that Adobe program use the PreciseScan technology from ABBYY smoothes pixelated characters on PDFs, thus improving the visual quality of documents for easier reading, archiving or better printing results.
Is it possible to apply some Nconvert filters to smooth images and get the same ...

Yes, you are right, a later PDF version wouldn't directly affect the image quality.
All difference is Antialias in Adobe Transformer pdf document. You can open two documents and see in 400% zoom.
Is it possible created pdf with Nconvert with Antialias like in Adobe Transformer?

Difference in quality: I created 2 pdf files from one png file (see attachment):
used Adobe Transformer (adobe_lomonosov.pdf) and Nconvert (nconvert -out pdf -o "nc_lomonosov.pdf" "lomonosov.png")
The quality of the file adobe_lomonosov.pdf is better

Hi everybody!
When I create pdf file from png pictures, I get pdf version 1.3 (Acrobat 4.x)
Is it possible upgrde pdf version to newer: 1.5-1.7 ??