You can access this screen by selecting "File | Import | HtmlHelp CHM Project". This feature will import your .HHP Project file, or if you do not have the source files, it will de-compile your CHM file and import it.
Fast-Help will do it's best to bring your files in in as perfect a way as possible, but there are some limitations during import. The first is that Fast-Help uses a single-source editor to compile to multiple formats. It is not a raw html editor, so some html features are not supported. De-compiling also adds an extra level of complexity. However, having said all this, Fast-Help will do the bulk of the work for you during import. You may have to tidy up some formatting but this will be a once only process. As once your data is within Fast-Help it can be maintained from there.
Select your .HHP file or your .CHM using the ellipsis buttons in the appropriate field.
Fill in your new Project details. Some of these will already be filled in for you. Click [Finish] and your Project will be imported.
Tidying up after Importing
The import process will try to reproduce your old help file as precisely as possible, but the nature of conversion means that not everything will be perfect. You may have some formatting to tidy up etc. To help with this there are some tools that you might find useful: