The Duchess and her husband, Prince William, toured the south Asian nation last month. It was the first major royal visit for years, with the terror threat behind the temporary absence.
After the visit, Kate wrote a note of thanks to Khadijah Shah, creative director of the Elan fashion brand.
Ms Shah posted the note on Twitter, adding her delight at having received it.
In the letter Kate said: “Thank you so much for all your help ahead of my tour to Pakistan.
“I am so grateful to you and your team for the wonderful selection you made for me to chose from.
The Duke and Duchess of Cambridge visited Pakistan in October
The Duchess of Cambridge playing cricket in Pakistan
“Having so many beautiful things did make decision making a little more difficult!
“Pakistan really is a wonderful country, which we both thoroughly enjoyed visiting and hope to return to one day soon.
“This comes with my warmest thanks and best wishes.”
The letter, dated November 5, was written on Kensington Palace writing paper.
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“Thank you so much for all your help ahead of my tour to Pakistan"
The Duke and Duchess visited Pakistan between October 14 and October 18.
For safety reasons details of the tour were not announced in advance.
They were accompanied on the visit by an entourage of 14 people.
For one of her engagements Kate wore a black and embroidered dress designed by Elan.
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“Pakistan really is a wonderful country, which we both thoroughly enjoyed visiting"
The Kate and Duchess of Cambridge in Islamabad
The dress, a kurti, had been designed in accordance with traditional Pakistani style.
On Twitter, Ms Shah expressed her joy at receiving the letter.
She commented: “I was delighted to have even been considered, this is just humbling to a whole different level.
“What’s most commendable is the consideration, grace and thoughtfulness of HRH the Duchess Catherine.
The Duke and Duchess of Cambridge got married in 2011
“It is no wonder that she is so respected and beloved.”
As part of the tour Kate visited a SOS Children’s Village project near Lahore.
Speaking to CNN she said: “There's so many vulnerable women here but they've really used their positivity and the support that the village here provides them.
The Duchess of Cambridge with members of the Pakistani army
“They have done it to support and protect the next generation of children in their care and give them the best possible start to their future lives.”
William and Kate returned to Britain aboard an RAF Voyager plane.
Ms Shah also used her Twitter account to compare Kate to Princess Diana commenting: “I absolutely adored Princess Diana growing up, and I’m just ecstatic that the Duchess is more and more like her.”