CamScanner provides you some PDF settings and you can set the default options to meet your requirement.

Tap the target document on “My Docs” page
Tap the button with three dots at the upper right corner of the page
Tap “PDF Settings” to enter the PDF Settings page

• Tap “Set PDF Password” to open a popup menu and input a password to encrypt the PDF file
• Tap “PDF Page Orientation” to choose the Portrait, Landscape or auto adjust one
• Tap “PDF Page Size” to edit the size of PDF. And CamScanner provides several industry standard sizes.
• Tap “PDF Page Margin” to add margin on PDF Page