The Muhimbi PDF Converter comes with extensive InfoPath support to deal with InfoPath attachments and Dynamic View Selection. However, most of the facilities provided are for 'real' InfoPath forms that are stored in a Forms or Document library.
SharePoint also allows the List Item Data Entry Form to be customised using InfoPath. However, data filled out using this facility is not stored as 'real' InfoPath Forms and therefore cannot be converted using Muhimbi's InfoPath to PDF / Word / Excel converter.
Fortunately List Items are rendered as HTML, even when customised via InfoPath, so as a workaround you can use the many HTML to PDF facilities provided by the Muhimbi PDF Converter for SharePoint to convert InfoPath based list items to PDF. When using SP2010 or later the results will improve dramatically when leaving out the 'SharePoint chrome' by adding '&IsDlg=1' to the URL of the list item that is being converted
Nintex Forms is a good alternative for customising List Items. For details about using the Muhimbi PDF Converter to convert those list items see this blog post.
If you are looking to include List Item attachments in your converted PDF then see this Knowledge Base entry.
Please note that HTML is not a format that is suited for output on printed media (including PDF). We do our very best to make things work, and render, as well as possible, but unfortunately we cannot make any guarantees, especially where it comes to third party products that are not under our control.
We regularly talk to the Nintex Forms team and their official position is that Nintex Forms is a data entry tool and not suitable for print or PDF output. Captured data should be embedded in MS-Word files and then converted using tools such as the Muhimbi PDF Converter as described in this blog post. Alternatively captured data can be placed in a template using Muhimbi's extensive watermarking facilities. Another possible solution is to create a 'string of HTML' in your workflow, place the various form fields in it, and send that string to our 'Convert HTML to PDF' workflow action.