You're making sense... big question is, did you send the book across as a PDF or did Calibre convert it to a MOBI/AZW file?
Either will work, but you'll get different results. Sometimes the PDF is better, sometimes the converted version.
Let me explain...
A PDF is fixed to individual pages, it's effectively an electronic "image" of a book - the pages are just the same as they are in the real book.
Now, if the real book has small pages (paperback books size), it will display on the 6" Kindle screen OK - each page in the book will be one screen in size.
However, if the real book is bigger - Letter or A4 in size, when you display it on a 6" screen, the pages will still be one screen in size, and as a result it's way too small to read.
An ebook, on the other hand (mobi or AZW) is the text of the book. It's not a fixed page size, so will scale to any screen (there will be more or less words on the screen depending upon the font you choose and the screen size). Navigation is by means of being able to jump through the chapters or sections of the book (which therefore depends on this information being encoded in the file).
Now, if you've taken a PDF and converted it to a mobi, you will probably have the variable size text, but you will still have all the "junk" that's at the top and bottom of each page - headers and footers, the page numbers and title etc - and you won't have any of the chapter information.
So, often with a PDF, your choices are either to transfer it as a PDF in which case you'll get a well formatted page which is too small to read, or convert it in which case you'll get words which are easy to read, but with headers/footers etc in the text, and no easy navigation.
I'm afraid all you can do is try both the PDF and the conversion, and see which you prefer for the particular book. There is no hard and fast rule, and sometimes both are pretty poor. PDF was never designed for e-book readers!
[I probably should explain that if you are prepared to put some work into it, you can do a good conversion. Calibre has a number of tools to remove headers and footers and detect chapters, but you need to tell it what to look for. Another approach is to convert PDF to RTF, open the RTF in Word, edit out the headers and footers, pick out the chapters or sections as headings, then convert the RTF to mobi/azw. A lot of work for a one-off book!]
Either will work, but you'll get different results. Sometimes the PDF is better, sometimes the converted version.
Let me explain...
A PDF is fixed to individual pages, it's effectively an electronic "image" of a book - the pages are just the same as they are in the real book.
Now, if the real book has small pages (paperback books size), it will display on the 6" Kindle screen OK - each page in the book will be one screen in size.
However, if the real book is bigger - Letter or A4 in size, when you display it on a 6" screen, the pages will still be one screen in size, and as a result it's way too small to read.
An ebook, on the other hand (mobi or AZW) is the text of the book. It's not a fixed page size, so will scale to any screen (there will be more or less words on the screen depending upon the font you choose and the screen size). Navigation is by means of being able to jump through the chapters or sections of the book (which therefore depends on this information being encoded in the file).
Now, if you've taken a PDF and converted it to a mobi, you will probably have the variable size text, but you will still have all the "junk" that's at the top and bottom of each page - headers and footers, the page numbers and title etc - and you won't have any of the chapter information.
So, often with a PDF, your choices are either to transfer it as a PDF in which case you'll get a well formatted page which is too small to read, or convert it in which case you'll get words which are easy to read, but with headers/footers etc in the text, and no easy navigation.
I'm afraid all you can do is try both the PDF and the conversion, and see which you prefer for the particular book. There is no hard and fast rule, and sometimes both are pretty poor. PDF was never designed for e-book readers!
[I probably should explain that if you are prepared to put some work into it, you can do a good conversion. Calibre has a number of tools to remove headers and footers and detect chapters, but you need to tell it what to look for. Another approach is to convert PDF to RTF, open the RTF in Word, edit out the headers and footers, pick out the chapters or sections as headings, then convert the RTF to mobi/azw. A lot of work for a one-off book!]