Upload all your PDF files to Dropbox or Google Drive or Microsoft OneDrive and then download them to your iPad. Download and install Adobe Reader for iPad from iTunes.
IfIf you don't feel like uploading PDF files via some web browser you can download and install Google Drive client or Microsoft OneDrive client or Dropbox client but thenon your PC. There exist Google Drive, Microsoft OneDrive and Dropbox app that you will have to download them via web browsercan install on iPad and download PDF files via this app.
You can also use Gmail and send an email to yourself and add all the PDF files as an attachment but there is a limit of 25 MB for the attachment when sending emails from Gmail.
Download and install Adobe Reader app for iPad to read PDF files...