I'm posting this because I could not find another question that dealt with my problem directly, but after A LOT of searching, and a few failed attempts, I did find the solution.
Problem: When creating a PDF from content copied to the clipboard from a webpage, everything on the page was way off-center, with almost no left margin.
Once the PDF was created, since there is no easy way to adjust page margins, the only way to center everything would have been one page at a time (for 24 pages), by dragging the page contents manually to the center of the page. I tried using the "Set Page Boxes" function, but I ended up with 24 blank pages. Yes, I could export the PDF as a Word document, and then reprint that Word document as a PDF, but I knew there had to be a simpler way.
Solution: When you create a PDF from a clipboard containing text (or in the case of the above document, text and images), Acrobat uses the settings for "Create PDF from Web Page."
Unfortunately, if you look up Convert clipboard content to PDF in Acrobat Help, it doesn't tell you that. AND the settings for "Create PDF from Web Page" are NOT included in the list of settings under Preferences > Convert to PDF. There is an HTML option in that list, but there are no editable settings for that file type (There are actually quite a few such file types listed there, and my question is, if there are no editable settings, why are they even listed under Preferences?). Batch Conversion of Text Files also uses the same settings.
So, here's how to do it:
Select File > Create > PDF from Web Page
Click on Settings
To adjust the default margins for new PDF files created from a clipboard containing text, select the Page Layout tab, and adjust the margins to your liking. Notice how small the Default right and left margins are... hence my problem.
Click on OK to save your new settings, and the simply Cancel out of the "Create PDF from Web Page" dialog box. If you read this page, it says you have to actually create at least one PDF file using the "Create PDF from Web Page" dialog in order for your settings to stick, but I never did, and my settings were saved just fine.
If you're copying basic text (or converting text files), that's all there is to it.
With web page content, there could still be a problem (as there was with this web page), if the content you've selected is not the full width of the web page. I think this has to do with the fact that web pages often use Content Style Sheets to format their page elements, and those styles are transferred when you copy that content to the clipboard. The PDF page margins are technically correct now, as you can see by the position of the image at the top of the page, but the text portion (at the bottom of the page) of the PDF only fills the same percentage of the text area (between the margins) as it did on the web page.
The only solution I have found if this happens, is to export the PDF as a Word document, and adjust the margins there. In the document I was working with in these examples, there were boatloads of different invisible subsections to the document, and each subsection had different settings for right and left indent, fonts, font sizes, etc., so there was a lot more to it than a simple 'copy & paste' type of procedure. Once I corrected all the different elements (and this one had a whole lot of weirdness going on), and then printed it as a new PDF, everything looked much better.
Hopefully this helps someone else find their answer much easier than I found mine
And of course, comments and suggestions are welcome.
Thanks for asking. Yes, with either the Crop tool or the Set Page Boxes tool, I could trim the page just fine, removing the excess from the right side, but as soon as I tried to add space to the left side, it just blanked out the whole page. It seemed like it should have worked, and maybe on a simple text file it would have. But that particular array of content proved to be most troublesome.
I also could have just cropped the page down to 6.5 x 11, and then centered it when I printed it.
My primary goal in searching for the answer, and my main reason for posting this, was for setting the margins for future documents (and to help others find those settings,too). Since I still had the web address, I could easily recreate the PDF once I figured out how to set the margins. Of course I didn't realize that there would still be problems once I got the settings right. Like I said, that particular web page seemed to have several unique difficulties.
Go for it. It's http://www.appliancerepair.net/washing-machine-repair-3.html Note the page is copyrighted, but it allows for copying or reprinting "brief passages," which is all I needed.
Frankly, it was a lot more fun working on getting the document to print the way I wanted it than it was working on the washing machine that I needed the document for. I needed to print the page because I didn't think it was such a hot idea to have my laptop sitting there while I was repairing the washer, and I didn't want to print all the garbage around the perimeter of the page (menus and such).
And printing it the way I wanted it proved to be a challenge, and I enjoy a good challenge now and then
After tinkering a bit with this, it would appear that the Insert from Clipboard command attempts to use the margins from whatever program the content came from. For example, when I pasted the content into Word and then copied it into Acrobat using the Insert from Clipboard command it launched Word in the background. So, it makes sense that the margins were taken from the Create PDF from web page command since this is where the content came from.