How to edit a PDF file in LibreOffice Draw or LibreOffice Writer without corrupting it?

PDF is not designed to be an editable format.

• Importing in LibreOffice Impress causes the PDF objects to be converted to LO objects that match as best as possible. This inevitably leads to changes because of incomplete mapping and conversion between the objects in these fundamentally different file formats. These changes may be less or more disrupting depending on the PDF.
• Importing in Gimp caused the PDF to be rendered in bitmap format. The looks are exactly the same, but an exported PDF will contain bitmap information. If vector objects were present in the original PDF, these will be lost.

Perhaps Xournal++ will suit your needs. You can add text, annotations and images to an existing PDF. The added content will be included as an additional layer, without changing the initial PDF data in any way.

Another way to add objects to an existing PDF would be to use command line tools. For example, pdftk with its stamp option allows to superimpose one PDF on another, useful for example to add page numbers, or eventually a graphic.

It is preferred, however, where possible, to work with source documents in the appropriate format for editing, and export the final version to PDF.

If you asked your question today is it safe to assume that you installed LibreOffice 7?

In any case you can just open the LibreOffice main launcher (from which you can create a document, spreadsheet, Drawing, or whatever, or, open a file.

Forget any import plugins. Just open any pdf file and LibreOffice will open it in Draw. Your pdf file will open. You can change text, add images and crop and/or size the images, move stuff around with no problem.

I'm not sure what you mean about "corrupting" your file. I suggest that as soon as you open your pdf file with LibreOffice you do immediately a "File Save as" and add a suffix to the file name such as " rev 1" or today's date.

This functionality has been around in LibreOffice for many versions now.

Vanadium's suggestions of using Xournal++ or Gimp are good, however I have found Xournal++ is quite limited and, for example, can only open files of a certain size, last time I used it. Now Gimp, on the other hand, is a VERY powerful and sophisticated tool, and you may find it has a significant learning curve.

IMHO LibreOffice is the best middle-of-the-road choice as it's powerful and quite intuitive to use.

Now there are many pdf editing programs available for Linux, here's one list mentioning some of the items above:

13 Best PDF editors for Linux

I have purchased Master pdf Editor and have used it for several months now and it works very well including Digital Signature Certificates.

I'm considering purchasing Quoppa for better security.