Update on this.......I have found an alternate way to get fully searchable PDF provided Text Width Factor and/or Oblique angle are at default values. This method does not require editing of the dwg file, just a re-publish of the PDF.
This is done by FORCING AutoCAD to substitute ttf for all the shx fonts.
1.) Delete the shx fonts from your workstation, including AutoCAD's default simplex.SHX. You have to delete....I tried renaming the font file like TAH-romans.shx and AutoCAD still found it. Then I renamed the folder to TAH-fonts and again AutoCAD still found it. I just DELETED all *.SHX files I found from the C: search.
2.) Edit the acad.fmp file and remove all entries. Save file as a blank file.
3.) Set the AutoCAD system variable FONTALT to your desired font. I used Arial.ttf.
4.) When AutoCAD loads it will try to find the fonts used in the dwg file using the path specified in the support search path settings. Since it cannot find them it will look at the acad.fmp file. Since this file is empty it will then look at the font defined in the text style again and attempt to find it in other places (folders). Since it still cannot find the file it will used the font stored in the AutoCAD FONTALT system variable which is Arial.ttf.
Mtext is shown in the text editor using the ttf equivalent of the shx font. For .ttf fonts it will first look in the acad.fmp which is empty, then at the font defined in the text style, then Windows will substitute a similar font which in my case is Arial.ttf.
Once the drawing is opened, fonts have been substituted, and any file output is done using the true type font(s). This works for DWF / DWFx to PDF or directly to PDF using simple PDF print drivers.
HOWEVER, if you have text with the Text Width Factor not equal to 1.0 and/or Text Oblique Angle not equal to 0.0 this text is still not searchable.
In our case 90% of our SHX based text becomes fully searchable where non of it did before
