I am looking to highlight duplicates in one workbook based on values from
another workbook

testbook! sheet1 A1:A10
values contain text string

linkedbook! sheet1 A1:A50
values contain text string

any duplicates in linkedbook! will be hightlighted in testbook!

I know how to use conditional formatting but need a little guidance when
linking to another workbook.

thank you in advance of any help