The text you see on a pdf page can be constructed in dozens of different ways, actually there are millions of users, using potentially hundreds if not thousands of different methods.
Update
The question is MacOS but for native cross platform you need to work in mime text/pdf to be universally useful. But by way of example how that's possible specifically in windows its possible to write line by line using say cmd here is a snippet of what was a few dozen lines :-)
echo %%PDF-1.0>demo.pdf
echo %%µ¶µ¶>>demo.pdf
echo/>>demo.pdf
for %%Z in (demo.pdf) do set "FZ1=%%~zZ"
echo 1 0 obj>>demo.pdf
echo ^<^</Type/Catalog/Pages 2 0 R^>^>>>demo.pdf
echo endobj>>demo.pdf
echo/>>demo.pdf
For the fuller "Feature Creep"ing of now over more than a 100 lines and counting see
https://github.com/GitHubRulesOK/MyNotes/raw/master/MAKE-PDF.cmd
Here is a JScript variant where "Hello World" can be read by your Phone or a Robot, HOWEVER due to web corruption the QRC will be distorted string characters, so a raw download is available at https://github.com/GitHubRulesOK/MyNotes/tree/master/JScriptSamples
var ByteStream = new ActiveXObject("ADODB.Stream");
ByteStream.Type = 2; // Writer
ByteStream.Charset = "Windows-1252"; //Best for PDF writer
var BS = ByteStream; // Abreviate for ease of edit
BS.Open();
BS.Position = 0;
BS.WriteText("%PDF-1.0\n");
BS.WriteText("%Åѧ¡\n");
BS.WriteText("1 0 obj <</Type/Catalog/Pages 2 0 R>> endobj\n");
BS.WriteText("2 0 obj <</Type/Pages/Count 1/Kids[3 0 R]>> endobj\n");
BS.WriteText("3 0 obj <</Type/Page/MediaBox[0 0 144 144]/Rotate 0/Resources<</XObject<</Img0 4 0 R>>>>/Contents 5 0 R/Parent 2 0 R>> endobj\n");
BS.WriteText("4 0 obj <</Type/XObject/Subtype/Image/Height 25/Width 24/BitsPerComponent 1/Length 75/ColorSpace[/Indexed/DeviceRGB 1<FF0000FFFFFF>]>> stream\n");
BS.WriteText('ÿÿÿÿÿÿÀmß[}ÑoEÑ[EÑqEßE}ÀUÿñÿÁ«Á¬ÛZcýÖÇÈ"}ÿÕïÀMsß`§Ñ]9ÑNÑE·ßLÇÀA[ÿÿÿÿÿÿ');
BS.WriteText("\nendstream\nendobj\n");
var Pos1 = "000000000"+BS.Position
BS.WriteText("5 0 obj <</Length 101>> stream\n");
BS.WriteText("q\n1 0 0 -1 18 54 cm\n35 0 0 -36 0 36 cm\n/Img0 Do\nQ\nq\n1 0 0 -1 71 144 cm\n70 0 0 -72 0 72 cm\n/Img0 Do\nQ\n");
BS.WriteText("\nendstream\nendobj\n\n");
var Pos2 = BS.Position
BS.WriteText("xref\n0 6\n");
BS.WriteText("0000000000 00001 f \n0000000015 00000 n \n0000000060 00000 n \n0000000111 00000 n \n0000000237 00000 n \n"+Pos1.slice(-10)+" 00000 n \n");
BS.WriteText("\ntrailer\n<</Size 6/Info<</Producer(JScrip2pdf)>>/Root 1 0 R>>\nstartxref\n"+Pos2+"\n%%EOF\n");
BS.SaveToFile("HelloWorldR&W.pdf", 2);
BS.Close();
However although plain text could be the simplest it is rarely used except to prove a conceptual point that it is possible. The rest of the time "Special Software" as you call it (a pdf generator/editor) will be used to compress the file objects, most frequently as different optimal binary streams.
So some text may be scanned pixels whilst other text may be line shapes that look like letters, or at other times plain letters without fonts but a named style, or even letters with the font included (embedded) in the file (the preferred option).
In many ways each page may be built different to the others and thus no two pdfs generally will use the same structure unless like a bank statement using a format that does not change much from month to month, even if the balance wobbles about.
So in summary the tool that will work best is the one that covers every single permutation that Adobe dreamed of, and still keep the result a valid Adobe PDF.
Thus Acrobat PRO 3D is on my shelf (even if not used from one year to the next)
There are many cheaper editors and ones I will use more often for small mods are Tracker Xchange and FreePDF PRO and both have different limitations.
Your choices for MacOS will be more limited thus search for the best you are willing to pay for.
