There are many apps that can open PDFs on iOS. However, the number of apps that have the ability to send the selected text in the PDF to the share menu is limited.
For example, iBook, Apple's standard app, allows you to add PDFs to your library for management and viewing, but when you tap the text of the selected PDF file, you will not find a "Share" option.
In such a case, the easiest way is to save it to Ikes via screenshot. However, saving the text to Ikes has some advantages, such as making it searchable.
One app that allows you to share the text of PDFs opened in iOS is the "File" app. This is a standard Apple app, so all iOS users can find it on their devices. This app allows you to manage and view documents stored in iCloud or on your device. When you open a PDF file in this app, you can highlight the text and choose "Share".