How to handle complex test results? Actually we are using D7 mostly for books and book pages like manuals.

We would like to link files like PDF and Excel to a Drupal book page but we have no experience how to manage to open those files from drupal or view their content in drupal.

Therefore I would appreciate instructions for eventually necessary modules and settings.

We have a browser extension in chrome for PDF and see them directly in the browser , but from a Drupal page (localhost:8080/drupal/?q=it/node/398), the link to that PDF first gets me to another page (drupal/?q=media/1242`) and I have to click again on the PDF icon to open it in the browser. Thaty's somewhat annoying.
Can anyone please indicate a direct way for PDF and for Excel files? Is it necessary to fit the browser for Excel? if yes, how?
Instead of "... save the differences in an Excel table ...", you might want to consider saving these data in an external database (MS SQL, MySql, Oracle, some PDO compliant database, etc).

And then use the Forena module to build custom queries to retrieve the data (directly from such database) and create custom reports from them. Those reports can then be exported in PDF or Excel. For that you just have to enable the desired Forena report options called "document format".

Refer to my answer to "How to download Database results as PDF or in EXCEL" for more details.