For exploring the inners of a PDF you also have RUPS[1] which is open source and easily installed in Linux through flathub[2].
> You may not deploy it on a network without disclosing the full source code of your own applications under the AGPL license. You must distribute all source code, including your own product and web-based applications.
They also have this delightful nagware encoded as a base64 string that spits this out in your logs [1]:
> You are using iText under the AGPL.
> If this is your intention, you have published your own source code as AGPL software too. Please let us know where to find your source code by sending a mail to agpl@apryse.com We'd be honored to add it to our list of AGPL projects built on top of iText and we'll explain how to remove this message from your error logs.
> If this wasn't your intention, you are probably using iText in a non-free environment. In this case, please contact us by filling out this form: http://itextpdf.com/sales If you are a customer, we'll explain how to install your license key to avoid this message. If you're not a customer, we'll explain the benefits of becoming a customer.
For using RUPS on a local computer you're probably safe, but I avoid the company because everything about their approach to the AGPL suggests that they chose it as a marketing technique for their paid products (with an extremely strong desire that it never be used commercially without pay), not out of a serious commitment to free software.
[0] https://itextpdf.com/how-buy/AGPLv3-license
[1] https://github.com/itext/itext-dotnet/blob/develop/itext/ite...
Stuff I do with it: Modify content streams, extract images/content, just investigate general structure of the pdf documents, remove pages, repair documents,... it's literally a swiss army knife when working with pdf's