Try this change:
And multipart file file = { read: '../testData/validPdfFile.pdf'}
Read this for a little more explanation: https://github.com/intuit/karate/tree/develop#multipart-file
Other than that you seem to be doing everything right. So it is up to your de-bugging skills now. Or give us a way to replicate: https://github.com/intuit/karate/wiki/How-to-Submit-an-Issue