Since the free 4.5 update of STFax is not available anymore from Haage & Partner,
I've uploaded it to Aminet.
When I contacted them I got the following reply:

No. We removed all 3rd party files long ago. However it think STFax is
shareware or freeware since a while. So you should find that through search
engines.


Mit freundlichen Grüßen
H&P-Supportteam

---- 

This archive contains an upgrade for STFax 4.1. If you don't have it,
have a look at Aminet

Changes in this update:

    4.5     20/09/00    - Added support for Diamond Multimedia voice command
                          set.
                        - Added ELSA MicroLink Office support for Independent
                          Mode.
                        - asyncio.library is used (if available) when transferring
                          files via XPR libraries (BBS transmissions).
                        - The check for files stored inside the modem memory
                          will be performed only once when STFax is started,
                          instead of each time the serial device is opened.
                        - The viewer will open using the last used scaling factor.
                        - Changed copyright from Active Technologies to
                          Haage & Partner.

PERMISSION  UID  GID    PACKED    SIZE  RATIO METHOD CRC     STAMP     NAME
---------- ----------- ------- ------- ------ ---------- ------------ ----------
[generic]                 3354    6095  55.0% -lh5- 3a34 Feb  2  2010 STFaxPatch40-45/History.txt.info
[generic]                 3355    6095  55.0% -lh5- b7fe Feb  2  2010 STFaxPatch40-45/LiesMich-UPD.info
[generic]                 2483    4792  51.8% -lh5- 4777 Sep 20  2000 STFaxPatch40-45/MUI/SpeedBarCfg.mcc
[generic]                 7233   15272  47.4% -lh5- 1662 Sep 20  2000 STFaxPatch40-45/MUI/SpeedButton.mcc
[generic]                27726   51828  53.5% -lh5- db8d Feb 29  2000 STFaxPatch40-45/MUI/Textinput.mcc
[generic]                 7057   16884  41.8% -lh5- 5bb4 Feb 29  2000 STFaxPatch40-45/MUI/Textinput.mcp
[generic]                 1916    3268  58.6% -lh5- 074f Feb 29  2000 STFaxPatch40-45/MUI/Textinputscroll.mcc
[generic]                 2475    3796  65.2% -lh5- 23d8 Aug 17  1999 STFaxPatch40-45/Patch
[generic]                20806   49260  42.2% -lh5- fe61 Feb 29  2000 STFaxPatch40-45/Phonebook
[generic]                  749    2233  33.5% -lh5- 1011 Oct  9  2000 STFaxPatch40-45/ReadMe-UPD
[generic]                 3349    6095  54.9% -lh5- 7299 Feb  2  2010 STFaxPatch40-45/ReadMe-UPD.info
[generic]               517927  609566  85.0% -lh5- 4942 Sep 27  2000 STFaxPatch40-45/STFax.patch
[generic]                 1202    6774  17.7% -lh5- 1f13 Sep 27  2000 STFaxPatch40-45/Update STFax
[generic]                 3081    5983  51.5% -lh5- c372 Jul  2  2001 STFaxPatch40-45/Update STFax.info
[generic]                 1770    2865  61.8% -lh5- 1a26 Jul  2  2001 STFaxPatch40-45.info
[generic]                11024   26192  42.1% -lh5- 2b16 Sep 27  2000 STFaxPatch40-45/Catalogs/deutsch/STFax.catalog
[generic]                 9664   23042  41.9% -lh5- d714 Sep 27  2000 STFaxPatch40-45/Catalogs/italiano/STFax.catalog
[generic]                21298   48536  43.9% -lh5- 3d46 Sep 20  2000 STFaxPatch40-45/FaxViewer
[generic]                 6193   22274  27.8% -lh5- 16bb Sep 20  2000 STFaxPatch40-45/History.txt
[generic]                30354   67724  44.8% -lh5- 4337 Sep 27  2000 STFaxPatch40-45/libs/STFax.library
[generic]                17687   30664  57.7% -lh5- c627 Feb 29  2000 STFaxPatch40-45/libs/vapor_toolkit.library
[generic]                  849    2380  35.7% -lh5- 2a03 Oct  9  2000 STFaxPatch40-45/LiesMich-UPD
[generic]                 3985    8648  46.1% -lh5- 8ec1 Sep 20  2000 STFaxPatch40-45/MUI/SpeedBar.mcc
[generic]                 3018    5876  51.4% -lh5- 3b25 Sep 20  2000 STFaxPatch40-45/MUI/SpeedBar.mcp
---------- ----------- ------- ------- ------ ---------- ------------ ----------
 Total        24 files  708555 1026142  69.1%            Mar 30  2012