I have a PSD file that I need to convert to an editable pdf, but it tells me that the file is too big, what do I do? It is for a publicity of 4 meters and I do not want to lose the quality
What is a »publicity of 4 meters« – a billboard?
If so why would the pdf need to be editable?
I do not know, because it is what they have asked me. I will also do it in another format
PDF is a common format used in printing, so a commercial printer asking for a pdf is nothing unusual. Normally you use the PDF/X subformat which has specific technical restrictions.
A printer would want an editable file because you'd be amazed at how often a designer sends files with errors that can be corrected (and the printer can of course charge money for those fixes.) This is not mandatory, you can send a file and tell them print as-is but if the job fails, again the printer charges money.
For a banner, they should have specific guidelines (CMYK or RGB and what color profile? What size and resolution? What about trapping? Registration marks? Should fonts be embedded in the pdf? What version of pdf?) that will apply to their equipment.
This is simply mutually exclusive and not possible. I'm not even sure what "editable PDF" is meant to imply, as PDFs have limited editing capabilities. Perhaps it would make sense if you actually explained what the requirements for the job at hand are soe people can advise on alternative solutions. This definitely cannot be brute-forced and there are no magic buttons that will make it work, either.
Well, what the printer has asked me for, I thought if that was possible but I see that it was not, I will talk to them again.
Without knowing what you are doing, a large print may need to be tiled (broken up into pieces) to deal with.
PDF is a finished format not for editing. Such artwork should be produced in InDesign, Photoshop or Illustrator (preferably a combination of these applications). For large posters, that are viewed from a distance the images can have a low resolution say 50PPI.