The pdf file should not be password protected. Did you download the pdf from Online version or did you use the Desktop program (& Windows or Mac)? Why do they need your pdf? That probably has more info and worksheets than they need. Did you email it? It is not safe to email any personal info especially your tax return.
It might be some security setting on their computer not letting them open pdf files.
Did you use the Online version or the Desktop CD/Download program? How are you sending them your return? As a pdf file?
If you used online....
What file did you download? Was it a .tax or .pdf or .txt file? If it downloads as a .txt file, try changing the .txt to .pdf or use a different browser to download it. It doesn't like Microsoft Edge so use something else like Chrome or Firefox.
How to get a copy after filing