There have been several users having problems with producing a PDF recently. Here is a link to one of the most recent threads where I list a lot of the potential fixes. As you said you have a large file I would suggest compressing the pictures as a first
step. Otherwise check this link: https://answers.microsoft.com/en-us/msoffice/forum/msoffice_publish-mso_win10-mso_365hp/publisher-pdf-problems/52f4d3bb-5591-4948-a751-d3608aeb3ed5
As to your formatting issues, MSFT changed the paragraph settings and the line spacing from 1.0 to 1.19 and 0pt before and after paragraphs to 0pt before and 6pt as of Publisher 2010. I think they wanted to be consistent with Word. As usual MSFT didn't offer
any explanation.
You can change the paragraph and line spacing by right clicking in the text box > change text > paragraph.
If you paste the entire page, including the formatted text boxes to a blank page I find the formatting will survive. Ctrl+A to select all on the page. Ctrl+shift+G to group all the elements together (or Home tab > arrange > group). Switch to the new document
and a new blank page and Ctrl+V to paste. The group of elements should be arranged correctly but if not you can drag the whole group around to where you want it and then Ctrl+shift+G to ungroup.
If you want to copy and paste just text then copy and paste to the new text box and you will see a small clipboard icon with (Ctrl) and a down arrow. Click the down arrow and choose
Keep source formatting to maintain your font, paragraph, line settings and other formatting intact.
If you end up with a font size that is smaller it may be that you have the Best Fit option checked. Go to Text box tools > Text group > Text Fit and uncheck Best fit and check
Do not autofit.
DavidF