If you have the difficulty in opening the pdf file, here is the summary of steps without screenshots.
Go to https://orcid.org and click “Sign in”
Login with your registered email and password to ORCID.
For those articles that have DOI link (URL usually starts with http://dx.doi.org/), Click “Search & link”à Click “CrossRef Metadata Search”à Click “Authorize”
Search your articles with DOI. If you find your articles, click “ADD TO ORCID”.
For those articles without DOI links, you can add the works manually. Click “Add Manually”, and fill in the form for each publication and click “Add to list.”