Is SharePoint Online suitable for creating a public job portal where anyone can upload their profile and search for job (just like job portal functionality)?
Unfortunately SharePoint Online have stopped serving new Office 365 subscribers to use the Public Website feature since March 2015. That doesn't mean you can't use SharePoint Online as a job portal site, since you still can share content to external users. Sharing to external users which are anonymous (i.e. a public website) isn't really supported in a straight forward way.
Therefore you shouldn't use SharePoint Online as a public website.
Starting January 2015, Microsoft is making changes to the SharePoint Online Public Website feature. Customers who currently use this feature will continue to have access to the feature for a minimum of two years after the changeover date of March 9, 2015. New customers who subscribe to Office 365 after the changeover date won't have access to this feature. Moving forward, Office 365 customers will have access to industry-leading third-party offerings that will enable them to have a public website that provides a complete online solution and presence.
SharePoint online is suitable to create public job portal, Where users can upload resume (documents) in documents library. and SharePoint advance search helps to fast search.
The Benefits of SharePoint Document Management
Easily track and find the documents you need. SharePoint can store multiple versions of a document, and it assigns each version a unique ID number. This prevents the wrong version of a document being retrieved and modified, as well as documents with the same file name being overwritten and lost forever.