Adobe Export PDF can create high-quality conversions, but the quality of converted document depends on the quality of the PDF file you start with.
For example, if your PDF file was originally authored in Microsoft Word or Excel and converted to PDF using the PDFMaker functionality of Adobe Acrobat, your PDF file contains a rich set of information that can be captured by Adobe Export PDF. This information includes relative positioning of tables, images, and even multicolumn text, as well as page, paragraph, and font attributes.
On the other hand, if your PDF file was originally authored using simpler PDF generation methods, such as “print to PDF” or “scan to PDF” options, Adobe Export PDF converts any recognizable text and then uses sophisticated conversion intelligence to preserve as much of the page layout as possible.
Likewise, poor quality scans, such as those where the scanned page is skewed, or there are smudges or marks on the page, are very difficult for Export PDF to convert. When possible, rescan those documents to produce a higher-quality scan.