I combined 60 pdfs into one file in adobe acrobat dc. Now i have one big file. when i email it, no one can open it. First it prompts to download adobe reader. After you do that, it says "cannot preview file type - please download for viewing" After you download it, it opens the file in a seperate window, asking you to download adobe reader again, which we already have. any help?
Have them completely download the file without opening it. Then have them use File>Open from within Reader itself to try and open it and see what happens.
It could be that their browser which may not even use Adobe Reader is trying to open it or it may be that they have a third party pdf viewer that is trying to open it. The above instructions will keep either of those things from happening and give you/us a better idea of what, if anything, we need to try next.
Did you combine files as a portfolio or as one file?
Yes my guess is you made a portfolio. Can be viewed only in Reader, not a browser or email app. It's an option; perhaps do it again with the option off.