What is an interactive PDF?
A PDF file can hold interactive elements of its own — hyperlinks and bookmarks added in a design tool, or form fields added in a PDF editor. That is still a file: it is usually downloaded, opened in whatever reader the person happens to have, and once it is sent you learn very little about what happened next.
HB Flipbook approaches it from the other direction. It publishes your existing PDF as an interactive web publication: readers open a link in the browser and turn pages on screen, the interactive elements you place are part of that hosted experience, the publication can be embedded in your own site, and reader analytics tell you how far people got.
To be clear about what it is not: HB Flipbook does not create fillable PDF forms, does not add Acrobat form fields and does not modify or re-save your source PDF. It leaves the file alone and builds the interactive publication around it. If you want the plain conversion story first, read how a PDF becomes a flipbook.