PDF Reader Markdown Doc Updates (#85)

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## Description

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Addressed feedback given during reviews of the markdown document.

## Context

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## Type of changes
Allows for easier understanding of the util.

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- [x] Refactoring (non-breaking change)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would change existing
functionality)
- [ ] Bug fix (non-breaking change which fixes an issue)

## Checklist

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- [x] I am familiar with the [contributing
guidelines](https://github.com/nhs-england-tools/playwright-python-blueprint/blob/main/CONTRIBUTING.md)
- [x] I have followed the code style of the project
- [ ] I have added tests to cover my changes (where appropriate)
- [x] I have updated the documentation accordingly
- [ ] This PR is a result of pair or mob programming

---

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Author: adrianoaru-nhs

docs/utility-guides/PDFReader.md

@@ -1,6 +1,6 @@
 # Utility Guide: PDF Reader
 
-The PDF Reader utility allows for reading of PDF files and performing specific tasks on them.
+The PDF Reader utility allows for reading PDF files and extracting NHS numbers from them.
 
 ## Table of Contents
 
@@ -10,26 +10,55 @@ The PDF Reader utility allows for reading of PDF files and performing specific t
     - [Extract NHS No From PDF](#extract-nhs-no-from-pdf)
       - [Required Arguments](#required-arguments)
       - [How This Function Works](#how-this-function-works)
+      - [Example Usage](#example-usage)
 
 ## Functions Overview
 
-For this utility we have the following functions/methods:
+For this utility, the following function is available:
 
 - `extract_nhs_no_from_pdf`
 
 ### Extract NHS No From PDF
 
-This is called to extract all NHS numbers from a PDF file.
-The way it finds an NHS number is by looking for the string **"NHS No:"**
+This function extracts all NHS numbers from a PDF file by searching for the string **"NHS No:"** on each page.
 
 #### Required Arguments
 
 - `file`:
   - Type: `str`
-  - This is the file path stored as a string.
+  - The file path to the PDF file as a string.
 
 #### How This Function Works
 
-1. It starts off by storing the PDF file as a PdfReader object, this is from the `pypdf` package.
-2. Then it loops through each page.
-3. If it finds the string *"NHS No"* in the page, it extracts it and removes any whitespaces, then adds it to a pandas DataFrame - `nhs_no_df`
+1. Loads the PDF file using the `PdfReader` object from the `pypdf` package.
+2. Loops through each page of the PDF.
+3. Searches for the string *"NHS No"* on each page.
+4. If found, extracts the NHS number, removes any whitespaces, and adds it to a pandas DataFrame (`nhs_no_df`).
+5. If no NHS numbers are found on that page, it goes to the next page.
+6. Returns the DataFrame containing all extracted NHS numbers.
+
+#### Example Usage
+
+You can use this utility to extract NHS numbers from a PDF file as part of the [`Batch Processing`](BatchProcessing.md) utility or by providing the file path as a string.
+
+**Extracting NHS numbers using a file path:**
+
+```python
+from utils.pdf_reader import extract_nhs_no_from_pdf
+file_path = "path/to/your/file.pdf"
+nhs_no_df = extract_nhs_no_from_pdf(file_path)
+```
+
+**Extracting NHS numbers using batch processing:**
+
+```python
+from utils.pdf_reader import extract_nhs_no_from_pdf
+get_subjects_from_pdf = True
+file = download_file.suggested_filename # This is done via playwright when the "Retrieve button" on a batch is clicked.
+
+nhs_no_df = (
+  extract_nhs_no_from_pdf(file)
+  if file.endswith(".pdf") and get_subjects_from_pdf
+  else None
+  )
+```