Pdf docs I used to be able to open now demand a password that I don't have

I recently moved from a PC to a Mac. Important pdfs that I use for my work don't work now that I've migrated to the Mac and now demand a password which I don't have. These pdfs can be opened from my PC and from another User I have on my Mac, but not from my own User account on the same Mac. Tried changing security settings to allow everyone to Read and Write. Didn't work. Unlocked the padlock. Didn't work. Changed Owner to my user, but still can't open my pdfs. Tried passwords from both User accounts. No dice. If I go into the other User account (which I opened as a test account using Migration Asst) I can open them. But if I want to open them in my User account on my Mac I need to move all my work pdfs into my other user account and then log out of one and into the other to just be able to open them. These are files I use every day. I'm thinking it's something to do with having 2 user accounts on my computer - one that used the Migration Asst and one that I manually transferred - is at the root of this. But how do I explain that I can send these online pdf forms to clients who happily open them, fill them out, and then send them back to me - where I then can't open them? I've spent hours on this. Any suggestions that I haven't already tried? Thanks!