I've customized pxCreatePDF activity by changing "call Code-Pega-PDF.AttachToWork" to "call Code-Pega-PDF.View" for downloading the PDF generated. I've created a section with the required format (all fields in Inline Grid double layouts). Upon passing this section to the customized pxCreatePDF activity, a PDF got generated with all the fields displayed in one single vertical line. PFA section snapshot and generated PDF.
Do you want me try the CSS change you suggested in the link or Free form layouts? I've tried creating a CSS file under Rule-File-Text and referred it in Custom CSS class field of Dynamic Layout's Presentation tab. But it didn't help. Also, I'm using Pega 7.3 and I didn't find Free form Layouts. Please advise.