Learn English – Single word for “pleasant to look at”

The adjective from reference is referential, but it wouldn't be appropriate here. I'd have thought 'for your convenience' would have been enough, but another formulation sometimes used is 'for ease of reference'.

Check, at least in British English, carries with it the suggestion that the reader should scrutinize the portfolio for errors. Look at is more general. Take a look at is less formal, and could be used in many contexts. Whatever verb you use, your message might have a more favourable reception if you soften the peremptory tone that a direct imperative conveys. You might therefore like to consider these alternatives, or variations of them, depending on the nature of your relationship with the client:

I should be grateful if you would examine the portfolio . . .

You might like to look through the portfiolio . . .

You might find it helpful to look through the portfiolio . . .