I have been researching this problem, and still have not found a solution for Linux. I did begin to browse the Serif forums, regarding PagePlus’s ability to create PDF/X-1a:2001 files. There are some who’ve had problems with the metadata when trying to upload their PagePlus PDF/X-1a:2001s to Lightning Source. That’s something I need to research further. Is there a workaround? Can I edit the metadata? How? Does it apply to PagePlus version 6 as well as version 5?
Another concern was whether or not I would have to reformat the entire book interior in either Acrobat Pro or PagePlus. This would have been discouraging because I’ve already done it in LibreOffice. I did discover that LO can export files in the .ps format, from which the PDF/X-1a:2001 files are made. That was a 1+ discovery. Since I’ve learned about metadata, however, I’d better make sure these are the same.
Another question is, how necessary is PDF/X-1a:2001 for a black and white manuscript? This particular pdf format is used for color images, which must be CMYK for printing, rather than RGB, as is the case for digital. Every now and then I read about some exception to LSI’s PDF/X-1a:2001 rule, which was successfully accepted, but no further information is provided.
This brings up another problem, i.e. changing all my RGB images to CMYK. The Gimp can do it, but requires details I am still unsure of.
I appear to have my research cut out for me. In the meantime, I am working on finishing up the front matter. I’m also getting ready to do an aloud read-through, to see if I can catch anything I messed up while adding photos and formatting the pages. Then I’ll work on adding page numbers to the index. I still have to do a cover as well. It’s been designed in my head, but hasn’t been created yet. I still seem to have a ton of work to do, yet the end is in sight.