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Unwanted characters in Acrobat PDF conversion of auto-detected Word fillable fields. Deleting fillable field characters using iTextSharp5

Acrobat DC, Office 365, iTextSharp5, Win10 Pro 64-bit
I have a Word document containing several pages of text and one empty TextBox in between two of the lines. I am attempting to use the Acrobat "Prepare Form" feature to convert that document to PDF with the TextBox as a fillable field, and Acrobat has no problem auto detecting the TextBox and making it fillable. The problem, however, is that the converted TextBox contains text from either the line of text above it or below it.
I've read that this is caused by placing the TextBox too close to those lines in the Word document and sure enough, by leaving three or four empty lines of space above and below the text box the issue goes away. However, that's an unacceptable amount of wasted space. I tried putting continuous section breaks above and below the TextBox in Word as well as typing spaces in the TextBox but that doesn't help. I also tried it with a 1x1 table instead of a TextBox but the same problem occurred.
I then tried deleting the unwanted text from the PDF TextBox field and saving it that way, which appeared to be a reasonable solution. However, when I used an iTextSharp5 program to detect the PDF's fillable fields it could no longer detect the empty field. I wouldn't mind leaving the original unwanted text in the PDF TextBox field if there were some way to remove it with iTextSharp, but it doesn't seem to have that ability.
Because I have many Word documents to convert to fillable PDF's and might need to update them occasionally, it simply isn't practical for me to manually add the fillable fields to the converted PDFs each time an update is needed. Any suggestions are welcome :-)

Getting Hyperlinks Working in Rich Text Box Using RTF

I am trying to format a hyperlink in a Rich Text Box using the Rich Text Format. I can get basic formatting working thanks to this answer, for example making text bold. However I cannot get the RTF formatted hyperlink to work. I found an example of making an RTF link here. However, when I try to put this in the Rich Text Box as seen below, it causes my application to crash. Any suggestions as to what i'm missing here?
string my_hyperlink_text = #"{\field{\*\fldinst HYPERLINK \"http://www.google.com/\"}{\fldrslt Google}}"
if (rtbControl is RichTextBox & rtbControl.Name == "name_of_control") // Making sure the control is a RichTextBox
{
RichTextBox rtb = rtbControl as RichTextBox;
rtb.Rtf = my_hyperlink_text;
}

An easy way for getting rtfs to work is to write your text in Microsoft word, copy & paste it to Wordpad and the saving it as a RTF from there.
The detour with MS Word is needed, because WordPad does not support entering links in the UI, although it handles them correctly when they come from other sources, like the clipboard. Also, MS Word creates massively bloated rtf.
The rtf file you create this way can then be opened in any text editor and can be used as a string constant in your program.
In your case, I suppose that the prefix and maybe the color table are missing and are causing the problem.
By the way: Wordpad is not much more than a wrapper around the Windows rtf control, i.e. the same control that you are using in your code.

Rich textbox that displays html like a web browser control

I am displaying text in a rich textbox and i want it to show the html formatting on the text. Is there a way to make a rich textbox display html.
If you push the button on the following link you will see how my out put displays, i would like it done in a rich textbox.
http://neil.fraser.name/software/diff_match_patch/svn/trunk/demos/demo_diff.html
Is there a way to build a rich textbox that can display html???

RTF encoding is different from HTML.
If not, then you need to write your own HTML to RTF converter or find something similar.
Writing Your Own RTF Converter. This guy gives a great breakdown of how the program works along with details of the conversion.
An Extended richtextbox control, Check this out. It may solve your solution

read word file with text and picture

i have a word(Office) file. this file content text and picture.
how can read this file and show in <textarea> </textarea>;

The best way to display rich content like word document on UI is through html. You can export your word document to HTML and render it to asp.net UI controls. If you prefer, textarea, you have to implement custom textarea to support images from word-html file.
Also, you can use WebBrowser control to display this word-html file instead of textarea.

I don't believe you can read this into a <textarea> as you ask. (I will watch to see if somebody else shows how, because I want to see that too...) I believe the closest result you will get is to open the document into an <iframe> with the application/msword content type. If you are looking for some flexiblity in this, wrap the space in a <div> and swap out <textarea> for <iframe> at the server when appropriate.

Header in richtext format and manipulating the rtf file

What is header in richtextbox format?? And how can we manipulate the rtf file.

To see how an RTF document looks in its raw form, save some text in an RTF-aware editor like wordpad, and then open it again in a plain text editor. For example, this RTF document:
Hello,
world!
becomes this when opened in plain text mode:
{\rtf1\ansi\ansicpg1252\deff0\deflang1030{\fonttbl{\f0\fswiss\fcharset0 Arial;}}
{\*\generator Msftedit 5.41.21.2509;}\viewkind4\uc1\pard\f0\fs20 Hello,\par
\b world\b0 !\par
}
Notice that there is a lot more text in the raw version than is visible when opened in an RTF-aware editor. If you want to manipulate the RTF document using raw string operations, you have to be careful to preserve the structure of this document otherwise it may become unreadable. It would be better to use an RTF parser to modify the document to avoid accidentally breaking it.

See the v1.6 RTF specification, including the Header part.
Obviously this relates to your previous questions today: again, I suggest that instead of trying to have a single document with multiple sections, you create separate documents.