T's, L's, and F's Omitted From PDF's in iBooks?

I have a particular publication that has these letters omitted and replaced by a gap, , especially in the middle of words. If I put it through OCR apps, it doesn't happen. Is there any way to adjust this in iBooks? Thanks much.

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#1 I think I know why

PDF files can be created by a wide variety of software. This includes the firmware in some printers. PDF files can consist of images, text or both.
The creator of your particular PDF probably selected his software defaults to export to PDF. Often these defaults do rudimentary OCR on the image, for purposes of indexing. The idea is that keyword searches can be conducted, but it is expected people will read the images of the PDF visually.
When you run the PDF through OCR, you are using higher quality OCR, such as what's found in An Open Book or Kurzweil 1000. They are able to adjust for poor contrast, and the letters you are missing are slender, or were printed with kerning, which jams them up against the following character. So the high quality OCR can recognize those skinny letters, but the low quality OCR that is the default for most PDF creation products cannot.

Hope this helps. Simply run the publication through higher OCR and save as RTF to make it take up much less space on your phone.

#2 Spot-on; thank you!

Thanks for that great explanation. I suspected this was the case. I'll just run it through Prizmo, then. :) Much appreciated.