Here I collect some useful applications have source code that can help you easily convert Tiff or Fax to PDF, some support windows, some support linux, some support both.

• Convert Tiff To Pdf:Tiff To PDF conversion Source Code.
• Scan2PDF:A utility for bulk scanning, converting the scanned pages to PDF and burning them on CD/DVD for archiving.
• Fax G3 TIFF to PDF converter

:fax2pdf provides a means to convert sets of G3 fax pages (encoded in a TIFF variant) into PDF. This can be used to convert fax pages received with eg. HylaFAX into a file format readily accessible/viewable with programs on most platforms.

• tiff2pdf, a part of gnuwin32 tiff, if you want to use it, you need both download:

tiff-3.8.2-1-bin.zip
and
tiff-3.8.2-1-dep.zip
or go to download the last version by yourself

• and there are some useful examples for Converting tiff files to PDF in iText(Java Version) and iTextSharp(C# version)

Tiff2Pdf.java: for detail
Tiff2Pdf.cs