Line spacing (leading) varies when I move text from pasteboard to page.

Hi Sandeep,

well, my assumption is that the text lines follow the document's baseline grid on the page.

Outside the page, the grid is not defined, so the text can follow its own definition of leading.

Read into this help article to understand the issue:

https://helpx.adobe.com/indesign/using/grids.html

View > Grids & Guides > Show/Hide Baseline Grid

You can define your paragraph formatting of your texts so that the text lines should follow the document's baseline grid.

To get you an idea how to disable the feature:

https://community.adobe.com/t5/indesign-discussions/how-do-i-stop-text-from-snapping-to-a-baseline-grid/m-p/10737265#M160636

Regards,
Uwe Laubender

( ACP )