[Phoenix84]

When I import books, in particular PDFs, they are being converted in-place by Calibre apparently.
This conversion on *import* actually is corrupting at least one PDF I have.

This is troublesome because I didn't expect it to tamper with the original imported file. When I proceed to open the PDF again in Adobe after import, I get errors when viewing every other page (error 110). The original does not exhibit this behavior. (File size is also different, which is why I know it's changing it.)
Note that I'm not using the PDF as a source for creating epub or mobi books. I'm using Calibre as a library to keep all my original formats just because everything is in one place. I have original epub and mobi formats I use for reading on devices.

Basically, I want to be able to store pristine copies of books in all the formats I care about, regardless of reading destination, and without Calibre altering them without my explicit permission.
It would be like if Lightroom altered my original RAW files.

I'm not sure if I can attach the PDF in question, since it's a paid book, but if the developers want a copy, let me know.

This is in Calibre 3.7.

EDIT: I found if I go into the Metadata editor, and manually remove and readd the PDF format in that dialog, the original is preserved.
I also noticed that the other formats are also edited, though I haven't encountered an issue with them to date.
These are DRM-free books (from Humble Bundle).

EDIT2: Well, I changed a bunch of options, and now it doesn't do it, but unfortunately I didn't keep track of what I changed.