SYMPTOM:
A user executes a grid report with numerous columns and observes that this report (because of its width) has a scrollbar at the bottom to allow the user to scroll left and right horizontally, as shown in the screen shot below:

When placing this grid report onto a Strategy 10.x Report Services document and switching to PDF mode, the user observes that the wide report is broken up onto separate PDF pages with wasted whitespace in between, as illustrated below:

Instead of breaking the report up onto separate pages, the user desires to keep the report on a single PDF page.
CAUSE:
By default, PDF documents have been configured to overflow horizontal grids onto separate PDF pages.
ACTION:
Edit the document and go to the top menu options: File > Page Setup… >Page Setup > Page, as seen in the screen shot below:

The Horizontal Fit setting is configured to overflow onto the 'Next page'. Change the Overflow setting to 'Below'.
Now, when the document is viewed in PDF mode, the report will overflow onto the same page:
