Both options will work. However, be aware that if you choose to select and mark the text with box function, there is a higher risk of inaccurately select elements or unwanted text that will then be part of the fact value within the iXBRL file.
If you choose the text-selection function, you will be able to select more precisely the text to tag. It is therefore recommended for tagging individual words and small paragraphs. Furthermore, if you are applying hypertags in the source file you will be able to edit and add text without adjusting hypertags. However, when using text selection it is important to keep in mind there can be no overlapping of tags applied to the text in both PDF and source file as this will create issues with converting and generate validation errors.
Finally, note that depending on the layout of the report (e.g. you have multiple columns) you would have to tag each column individually so that the text in the 'fact value' is displayed correctly.
For a more detailed guide on how to perform Hypertagging in the PDF, please see this guide